Bearing unit and rotary drive using the same

ABSTRACT

A bearing unit for rotatably supporting a shaft comprises a seamless holding member with a gap allowing a shaft to run through and extend to the outside, a bearing arranged in the inside of the holding member to rotatably support the shaft so as to make it radially revolvable, an anti-shaft-release member fitted to the shaft so as to abut the bearing in order to prevent the shaft from slipping away in the thrusting direction and a space-forming member arranged in the inside of the holding member so as to secure a space around the anti-shaft-release member. A bearing unit may further comprise an lubricating oil seal member and the space-forming member may be used to form a passage way for lubricating oil to prevent lubricating oil from leaking.

TECHNICAL FIELD

This invention relates to a bearing unit and a rotary drive using such abearing unit.

This is a divisional of application Ser. No. 10/506,433, filed Apr. 4,2005, the entire contents of which is hereby incorporated by reference.

This application claims the priority of co-pending Japanese PatentApplication No. 2003-300529 dated Aug. 25, 2003, Japanese PatentApplication No. 2003-053231 dated Feb. 28, 2003 and Japanese PatentApplication No. 2003-004928 dated Jan. 10, 2003, all filed in Japan.These patent applications are incorporated herein by reference.

BACKGROUND ART

A bearing unit rotatably supports a shaft and is typically arranged in arotary drive such as a fan motor.

A bearing unit of the type under consideration is used with an I-shapedshaft (also referred to as straight shaft) that is rotatably supportedby using lubricating oil. Japanese Patent Publication No. 3265906describes such a bearing unit. The bearing unit 540 disclosed in thepatent publication has a configuration as shown in FIG. 1 of theaccompanying drawings. Referring to FIG. 1, the bearing unit 540rotatably supports a shaft 541 by means of a radial bearing 542 and athrust bearing 543. The radial bearing 542 is supported by a holdingmember 544 while the thrust bearing 542 is supported by a bottom plate545. An anti-shaft-release member 546 is fitted to the shaft 541.

Since it is impossible to insert the anti-shaft-release member 546 inthe last step of assembly due to the structure of the bearing unit 540,it is necessary to employ a step of mounting the thrust bearing 543 andthe bottom plate 545 in the holding member 544 as the last assemblingstep. In other words, because of the use of such an assembling step, thehousing of the bearing unit 540 needs to comprise a plurality ofmembers, which include the holding member 544 and the bottom plate 545,for the purpose of providing the shaft 541 with the anti-shaft-releasemember 546. Then, it is difficult to completely seal the binding section548 of the holding member 544 and the bottom plate 545. As a result, thelubricating oil filled in the inside can leak out.

Additionally, end facet 547 of the radial bearing 542 is exposed to theoutside and lubricating oil can highly possibly disperse and evaporatefrom there.

Since the known bearing unit 540 comprises the anti-shaft-release member546 for the shaft 541, the housing that takes the role of surroundingthe bearing unit 540 and preventing lubricating oil from leaking anddispersing is formed by a plurality of members. Therefore, there is aproblem that lubricating oil is apt to leak out through the bindingsections of various members of the housing. There is also a problem thatsuch a bearing unit needs to be prepared by way of complex steps toconsequently raise the manufacturing cost.

Another known proposed bearing unit employs as a bearing means forsupporting a shaft made of metal such as stainless steel a radialbearing and a thrust bearing that are sintered and oil-impregnatedbearings or hydrodynamic fluid bearings and supported by respectivehousing members made of metal such as brass, of which the radial bearingis provided with a seal member for minimizing the leakage of thelubricating oil filled in an inner peripheral section thereof. With theproposed bearing unit, the shaft is rotatably supported by the radialbearing and the thrust bearing so that the shaft is supported androtatable relative to the housing members.

With this bearing unit, lubricating oil is indispensable for the shaftto revolve smoothly and prevented from leaking out by a seal member.Lubricating oil can ooze out through every gap and leak to the outsideof the bearing unit to shorten the service life of the bearing unit.Therefore, the binding sections of members of the bearing unit need tobe hermetically sealed. For this purpose, the applicant of the presentinvention proposed a bearing unit wherein the binding section of ametal-made housing member and a seal member is hermetically sealed bymeans of a UV-ray set type adhesive agent in Japanese Patent ApplicationNo. 2001-289568 and another bearing unit wherein a resin-made housingmember is used and integrally molded with a seal member in JapanesePatent Application No. 2002-34331.

However, with such bearing units, it is difficult to satisfactorilymaintain the stability and the reliability.

For example, when a housing member and a seal member are preparedseparately, it is difficult to completely bond or bind them together andhence to reliably prevent lubricating oil from leaking through thebinding section thereof. Additionally, it is a highly complex anddifficult operation to uniformly apply a polymeric packing material suchas adhesive to the entire periphery of the binding section. It is alsodifficult to see if the binding section is completely sealed withoutmicro-gaps. The net result will be either unsatisfactory reliability orprohibitive cost.

Leakage of lubricating oil cause to result in an unstable service life,a reduced reliability of the bearing unit and/or adverse effects (suchas chemical attack phenomenon) on the externally disposed components ofthe bearing unit. For instance, when such a bearing unit is applied to ahard disc drive (HDD), leakage of lubricating oil containing organicsubstances cause to give rise to stiction and haze (a clouded discsurface).

When a housing member and a seal member are integrally molded, no gap isproduced between them. However, if the gap between the seal member,which is now part of the housing member, and the shaft needs to beminimized when the housing is molded with the shaft supported by abearing unit, it is difficult to guarantee the accuracy of minimizingthe gap. For instance, any variance in the gap between the seal sectionand the shaft can influence the level of the oil surface and hence, ifthe volume of oil is large, lubricating oil cause to disperse to theoutside when the oil temperature rises and/or when the ambient pressurechanges.

The PCT Application Laid-Open No. WO03/027521 describes another knownbearing unit adapted to rotatably support a rotary shaft. Referring toFIG. 2 of the accompanying drawings, the bearing unit 660 is able toreliably prevent viscous fluid from leaking to the outside of thehousing that is filled with viscous fluid even when the internalpressure of the housing changes due to a change in the environmentalfactors including atmospheric pressure and/or ambient temperature.

The bearing unit 660 comprises a radial bearing 644 and a thrust bearing650, by which a rotary shaft 641 is rotatably supported, air releasingpassage sections 662 being arranged between a housing 661 that is filledwith lubricating oil 653 and the inner peripheral surface of an outersleeve 667 that covers the housing 661.

The air releasing passage sections 662 are provided in order to preventlubricating oil 653 from leaking to the outside of the bearing unit 660when the atmospheric pressure falls due to an altitude change and theair inside the housing 661 expands. The housing 661 may be provided withone or more than one air releasing passage sections 662. In theillustrated bearing unit 660, three air releasing passage sections 662are arranged on the outer periphery of the housing 661 and angularlyseparated from each other at regular intervals. The air releasingpassage sections 662 can be formed in a simple manner when the housing661 is produced by outsert molding along with the thrust bearing 650that contains the radial bearing 644. If the air releasing passagesections 662 have a relatively complex profile, they can be formed whenthe housing 661 and the thrust bearing 650 are molded by using syntheticresin.

With the provision of such air releasing passage sections 662, it ispossible to release the air that comes into the bearing unit when therotary shaft 641 is inserted into the radial bearing 644 and placed inposition.

In the bearing unit 660, each of the air releasing passage sections 662has a first passage way 663 and a second passage way 664. The firstpassage way 663 is formed to extend along a radial direction of thehousing 661 from an internal space 665 that is located near the thrustbearing 650. The inner end of the first passage way 663 is connected tothe internal space 665 where the thrust bearing 650, which projects fromthe bottom closure section 647 of the housing 661, is located. The outerend of the first passage way 663 is connected to the second passage way664. The second passage way 664 is exposed to the outer peripheralsurface of the housing 661 and extends along the axial direction of thehousing 661. While the air releasing passage section 662 including thefirst passage way 663 and the second passage way 664 has a relativelycomplex profile, it can be formed with ease when the housing 661 and thethrust bearing 650 are molded from synthetic resin.

As the bearing unit 660 is provided with the air releasing passagesection 662, the inside of the housing 661 is not hermetically sealed.Therefore, the internal static pressure of the housing 661 does not fallwhen the rotary shaft 641 revolves relative to the housing 661 and hencethe air remaining in the housing 661 does not expand to force out thelubricating oil in the inside.

The bearing unit 660 communicates with the outside by way of a pluralityof sections including the air releasing passage sections 662 and theexposed part of the rotary shaft 641. In other words, the former operateas an air inlet port while the latter operates as an air outlet port sothat lubricating oil cause to disperse when impact is applied to thebearing unit 660. In short, the bearing unit 660 is vulnerable toimpact.

Japanese Patent Application Laid-Open Publication No. 2000-352414describes still another bearing unit for rotatably supporting a rotaryshaft. As shown in FIG. 3 of the accompanying drawings, the bearing unit680 of the above cited patent document is adapted to rotatably support arotary shaft 681 and comprises a radial bearing 682 for supporting therotary shaft 681 in a peripheral direction, a thrust bearing 683 forsupporting the rotary shaft 681 in a thrusting direction and a housing685 containing the radial bearing 682 and the thrust bearing 683.

The radial bearing 682 of the bearing unit 680 operates as hydrodynamicfluid bearing with the lubricating oil filled in the housing 685, whichlubricating oil is viscous fluid. Dynamic pressure generating grooves684 are formed on the inner peripheral surface of the radial bearing682, along which the rotary shaft 681 is inserted.

The radial bearing 682 is provided on the outer peripheral surfacethereof with groove-shaped axial air passage ways 686 and groove-shapedradial air passage ways 687 that are used as air releasing passage wayswhen inserting the shaft member into the inner space of the bearing mainbody.

As shown in FIG. 3, housing 685 that contains the radial bearing 682,which by turn supports the rotary shaft 681, has a bottomed hollowcylindrical profile so as to surround the lateral surface and the bottomsurface of the radial bearing 682, which also has a hollow cylindricalprofile.

A compressed resilient body 688 is arranged in the upper opening of thehousing 685 so as to be pressed against the inner peripheral surface ofthe housing 685 to operate as caulking member.

The rotary shaft 681 is inserted into the housing 685 of the bearingunit 680 that is caulked by the resilient body 688. At this time, air isreleased from the inside of the housing 685 to the outside by way of theaxial air passage ways 686 and the radial air passage ways 687 so thatthe operation of inserting the rotary shaft 681 can be conductedsmoothly.

Since the bearing main body is surrounded by two members of a housing685 and a resilient body 688 in the bearing unit 680 of FIG. 3,lubricating oil is caused to ooze out through the junction of thehousing 685 and the resilient body 688.

DISCLOSURE OF THE INVENTION

Therefore, it is an object of the present invention to provide a bearingunit that addresses the problems of the bearing units that have beenproposed to date and a rotary drive using such a bearing unit.

Another object of the present invention is to provide a bearing unitthat is compact and highly reliable and can enjoy a long service lifeand a rotary drive using such a bearing unit.

Still another object of the present invention is to provide a bearingunit that can prevent the shaft supported by the bearings of the bearingunit from slipping away and the lubricating oil contained in the insideof the bearing unit from leaking and a rotary drive using such a bearingunit.

Still another object of the present invention is to provide a bearingunit that can prevent a phenomenon of leakage of the viscous fluid suchas lubricating oil that is filled in the housing of the bearing unitfrom taking place and show an excellent lubricating performance when theshaft is driven to revolve relative to the housing to reduce theinternal pressure of the housing and expand the residual air in thehousing and a rotary drive using such a bearing unit.

Still another object of the present invention is to provide a bearingunit from which viscous fluid such as lubricating oil can hardlydisperse when impact is applied thereto and a rotary drive using such abearing unit.

A further object of the present invention is to provide a bearing unitthat can effectively prevent viscous fluid such as lubricating oil fromoozing out from the housing of the bearing unit that surrounds thebearings of the unit and a rotary drive using such a bearing unit.

In an aspect of the present invention, the above objects are achieved byproviding a bearing unit for rotatably supporting a shaft, the bearingunit comprising: a seamless holding member with a gap allowing a shaftto run through and extend to the outside; a bearing arranged in theinside of the holding member to support the shaft so as to make itradially revolvable; an anti-shaft-release member fitted to the shaft soas to abut the bearing in order to prevent the shaft from slipping awayin the thrusting direction; and a space-forming member arranged in theinside of the holding member so as to secure a space around theanti-shaft-release member.

A bearing unit according to the invention comprises a holding member andall the remaining components of the bearing unit are arranged in theinside of the holding member. The bearing unit radially supports theshaft so as to allow the latter to revolve. The anti-shaft-releasemember is fitted to the shaft so as to abut the bearing and prevent theshaft from slipping away along the thrusting direction. Thespace-forming member is arranged inside the holding member. Thespace-forming member is adapted to secure space around theanti-shaft-release member. With this arrangement of providing such aspace-forming member, a small anti-shaft-release member can be arrangedinside the holding member of the bearing unit. As a result, it ispossible to downsize the rotary drive, which may be a motor, to be usedwith the bearing unit. Since the bearing unit comprises theanti-shaft-release member and can prevent the shaft from slipping awayin the assembled state, it is easy to handle the bearing unit when it isfitted to a rotary drive.

The holding member is formed as seamless member with an opening thatallows the corresponding end of the shaft to project to the outside andhence it would not allow lubricating oil from leaking out. Thus, it ispossible to provide a compact and highly reliable bearing unit that canenjoy a long service life.

The number of components is reduced when the anti-shaft-release memberand the shaft are formed integrally with each other. The holding memberis made of a polymeric material and the gap is defined by the holdingmember and the shaft at the position where the shaft extends from theholding member.

The space-forming member of a bearing unit according to the invention ismade of a polymeric material and operates as a thrust bearing forrotatably supporting the shaft at an end of the latter in the thrustingdirection. The end of the shaft is made to show a spherical profile andthe thrust bearing is a pivot bearing.

With this arrangement, the space-forming member can not only securespace around the anti-shaft-release member but also rotatably supportthe corresponding end of the shaft as pivot bearing in the thrustingdirection so that it is possible to reduce the number of components anddownsize the bearing unit.

A bearing unit according to the invention can generate dynamic pressureas the shaft revolves because it is provided with dynamic pressuregenerating grooves on the outer peripheral surface of the shaft or onthe inner peripheral surface of the bearing.

A bearing unit according to the invention can generate dynamic pressureas the shaft revolves because additionally the surface of theanti-shaft-release member or the surface of the space-forming memberarranged vis-à-vis the anti-shaft-release member is provided withdynamic pressure generating grooves.

Of a bearing unit according to the invention, the shaft and thespace-forming member are made of an electrically conductive material andthe space-forming member is exposed to the outside through the holdingmember. With this arrangement, the shaft can be grounded by way of thespace-forming member in order to release any static electricity to theoutside.

In another aspect of the present invention, there is provided a rotarydrive including a bearing unit for rotataby supporting a shaft, therotary drive comprising: a seamless holding member with a gap allowing ashaft to run through and extend to the outside; a bearing arranged inthe inside of the holding member to support the shaft so as to make itradially revolvable; an anti-shaft-release member fitted to the shaft soas to abut the bearing in order to prevent the shaft from slipping awayin the thrusting direction; and a space-forming member arranged in theinside of the holding member so as to secure a space around theanti-shaft-release member.

The bearing of this rotary drive is arranged in the inside of theholding member. The bearing radially supports the shaft so as to allowthe latter to revolve. The anti-shaft-release member is fitted to theshaft so as to abut the bearing and prevent the shaft from slipping awayalong the thrusting direction.

The space-forming member is arranged inside the holding member. Thespace-forming member is adapted to secure space around theanti-shaft-release member. With this arrangement of providing such aspace-forming member, the anti-shaft-release member is arranged insidethe holding member of the bearing unit. As a result, it is possible todownsize the rotary drive, which may be a motor, to be used with thebearing unit.

In still another aspect of the invention, there is provided a bearingunit having a shaft and a bearing means for rotatably supporting theshaft, the bearing unit comprising: a lubricating oil seal memberarranged between the shaft and the bearing means with a gap interposedbetween them; and a synthetic resin made housing for peripherallyholding the lubricating oil seal member and the bearing means.

With a bearing unit according to the invention and having theabove-defined configuration, it is possible to realize a seamlessstructure that binds the seal member and holding means without any gapbetween them by peripherally holding the seal member by the resin madehousing. Thus, it is no longer necessary to seal the gap between theseal member and the housing by means of an adhesive agent or the like. Anecessary gap is guaranteed between the seal member and the shaft bysecuring the processing precision and the molding precision of themember so that the variance of the gap can be sufficiently reduced.

In still another aspect of the invention, there is provided a bearingunit comprising: a shaft; a radial bearing for peripherally supportingthe shaft; a thrust bearing for supporting an end of the shaft in thethrusting direction thereof; a space-forming member arranged outside theradial bearing and the thrust bearing; a housing having thespace-forming member in the inside and hermetically sealed except ashaft receiving hole through which the shaft is made to extend; viscousfluid filled in the housing; and a communication passage way arrangedbetween the space-forming member and the radial bearing so as to makethe end in the thrusting direction of the shaft projecting from theradial bearing and the other end of the shaft communicate with eachother.

With a bearing unit according to the invention and having the abovedescribed configuration, the end in the thrusting direction of the shaftprojecting from the radial bearing that is located at the closed side ofthe shaft and the other end of the shaft projecting from the radialbearing that is located at the open side of the shaft where the shaftreceiving hole is provided are made to communicate with each other byway of a communication passage way. Therefore, when the shaft is drivento revolve relative to the housing, the pressure reduction at the closedside of the shaft is minimized because the closed side of the shaft ismade to communicate with the open side of the shaft. As the pressurereduction at the closed side is minimized, the residual air in thehousing is suppressed against expanding to prevent viscous fluid such aslubricating oil from being forced to leak out.

With a bearing unit according to the invention and having the abovedescribed configuration, while the closed side end and the open side ofthe shaft are held in communication with each other, the shaft isexposed to the outside only at the other end that projects in the thrustdirection from the radial bearing located at the closed side of theshaft through a minimally dimensioned gap of the shaft receiving hole.In other words, the communication passage way is formed in the housing,which is hermetically sealed except the shaft receiving hole so that theviscous fluid such as lubricating oil that is contained therein isprevented from dispersing by impact and also from oozing out.

Other objects and advantages of the present invention will becomeapparent from the following description that is made by referring to theaccompanying drawings that illustrate preferred embodiments of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross sectional view of a known bearing unit;

FIG. 2 is a schematic cross sectional view of another known bearingunit;

FIG. 3 is a schematic cross sectional view of still another knownbearing unit;

FIG. 4 is a schematic perspective view of an electronic devicecomprising a bearing unit according to the invention;

FIG. 5 is a schematic cross sectional view of the electronic device ofFIG. 4 taken along line V-V in FIG. 4;

FIG. 6 is a schematic perspective view of a fan motor;

FIG. 7 is a schematic cross sectional view of the rotor and the statorof a fan motor;

FIG. 8 is a schematic cross sectional view of an embodiment of bearingunit according to the invention that is used in the fan motor of FIG. 7;

FIGS. 9A through 9C are schematic cross sectional views of the bearingunit of FIG. 8, showing assembling steps thereof;

FIG. 10 is a schematic cross sectional view of another embodiment ofbearing unit according to the invention;

FIG. 11 is a schematic cross sectional view of still another embodimentof bearing unit according to the invention;

FIGS. 12A and 12B are schematic cross sectional views of still anotherembodiment of bearing unit according to the invention;

FIGS. 13A through 13D are schematic cross sectional views of theembodiment of bearing unit of FIGS. 12A and 12B, showing assemblingsteps thereof;

FIG. 14 is a schematic cross sectional view of still another embodimentof bearing unit according to the invention;

FIG. 15 is a schematic cross sectional view of still another embodimentof bearing unit according to the invention;

FIG. 16 is a schematic cross sectional view of an embodiment of rotarydrive according to the invention and comprising a bearing unit accordingto the invention;

FIG. 17 is a schematic cross sectional view of another embodiment ofrotary drive according to the invention, which is a motor, andcomprising a bearing unit according to the invention;

FIG. 18 is a schematic cross sectional view of an embodiment of bearingunit according to the invention taken along line Y-Y′ in FIG. 19;

FIG. 19 is a schematic cross sectional view of the embodiment of FIG. 18taken along line X-X′ in FIG. 18;

FIG. 20 is a schematic perspective view of dynamic pressure generatinggrooves formed on the inner peripheral surface of the radial bearing ofa bearing unit according to the invention;

FIG. 21 is a schematic perspective view of a communication passage waythat can be formed between the space-forming member and the radialbearing of a bearing unit according to the invention, showing theprofile thereof;

FIG. 22 is a schematic bottom view of second grooves that can be formedon the bottom surface of the radial bearing so as to operate ascommunication passage way of a bearing unit according to the invention;

FIG. 23 is a schematic perspective view of another communication passageway that can be formed between the space-forming member and the radialbearing of a bearing unit according to the invention, showing theprofile thereof;

FIG. 24 is a schematic plan view of other second grooves that can beformed on the bottom surface side of the space-forming member so as tooperate as communication passage way of a bearing unit according to theinvention;

FIG. 25 is a schematic cross sectional view of the gap defined by theouter peripheral surface of the rotary shaft and inner peripheralsurface of the shaft receiving hole formed through the housing of abearing unit according to the invention;

FIG. 26 is a schematic illustration of the capillary phenomenon offluid;

FIG. 27 is a schematic cross sectional view of the lubricating oil thathas come into the gap formed between the outer peripheral surface of therotary shaft and the inner peripheral surface of the shaft receivinghole of a bearing unit according to the invention;

FIG. 28 is a schematic longitudinal cross sectional view of the gapformed between the outer peripheral surface of the rotary shaft and theinner peripheral surface of the shaft receiving hole of a bearing unitaccording to the invention, illustrating the pressure difference betweenparts of the tapered section of the rotary shaft having differentdiameters;

FIG. 29 is a schematic longitudinal cross sectional view of the gapformed between the outer peripheral surface of the rotary shaft and theinner peripheral surface of the shaft receiving hole of a bearing unitaccording to the invention, illustrating how air is drawn into thelubricating oil that has come into the gap;

FIG. 30 is a schematic transversal cross sectional view of the gapformed between the outer peripheral surface of the rotary shaft and theinner peripheral surface of the shaft receiving hole of a bearing unitaccording to the invention, illustrating that the lubricating oil thathas come into the gap is cut apart;

FIG. 31 is a schematic longitudinal cross sectional view of the rotaryshaft received in the shaft receiving hole of the housing of a bearingunit according to the invention, showing that the rotary shaft iseccentric relative to the shaft receiving hole;

FIG. 32 is a schematic cross sectional view of the rotary shaft receivedin the shaft receiving hole of the housing of a bearing unit accordingto the invention, showing the lubricating oil that has come into the gapbetween them when the rotary shaft is eccentric relative to the shaftreceiving hole;

FIG. 33 is a schematic cross sectional view of the third embodiment ofbearing unit according to the invention, in which the shaft receivinghole of the housing is tapered;

FIG. 34 is a schematic illustration of the temporary assembling step inthe process of manufacturing a bearing unit according to the inventionillustrated in FIG. 19;

FIG. 35 is a schematic illustration of the step of outsert molding thehousing in the process of manufacturing a bearing unit according to theinvention;

FIG. 36 is a schematic illustration of the step of inserting the rotaryshaft into the housing in the process of manufacturing a bearing unitaccording to the invention;

FIG. 37 is a schematic illustration of the step of filling lubricatingoil in the process of manufacturing a bearing unit according to theinvention; and

FIG. 38 is a schematic cross sectional view of still another embodimentof bearing unit according to the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, preferred embodiments of the present invention will be described byreferring to the accompanying drawings.

A bearing unit according to the invention can typically find anapplication in a portable computer 1 as shown in FIG. 4.

Referring to FIG. 4, the computer 1 has a display section 2 and a mainbody 3. The display section 2 is rotatably linked to the main body 3 bymeans of a link section 4. The main body 3 has a keyboard 5 and acabinet 12. A heat-emitting device 10 is arranged in the cabinet 12.

FIG. 5 is a schematic cross sectional view of the cabinet 12 of FIG. 4taken along line V-V in FIG. 4. FIG. 6 is a schematic perspective viewof the heat-emitting device 10 arranged in the cabinet 12 of FIG. 5.

As shown in FIG. 5, the heat-emitting device 10 is contained in thecabinet 12. The heat-emitting device 10 has a configuration as shown inFIG. 6. The heat-emitting device 10 is also referred to as coolingdevice and comprises a metal made base 20, a motor 30, a fan 34, that isa rotary body, a fan case 36 and a heat sink 38.

One of the surfaces, or surface 21, of the base 20 includes a firstfitting surface 50, a second fitting surface 52 and a third fittingsurface 54. When put together, the first fitting surface 50, the secondfitting surface 52 and the third fitting surface 54 form a substantiallyL-shaped surface. A heat emitting element 40 is fitted to the firstfitting surface 50 by way of a heat transmitting seal 44. The heatemitting element 40 may typically be a CPU (central processing unit)that emits heat when it is electrically energized to operate.

The fan case 36 and the motor 30 are rigidly fitted to the secondfitting surface 52. The fan 34 and the motor 30 are contained in theinside of the fan case 36. The fan case 36 has a circular hole 48. Thecircular hole 48 is formed at a position of the fan case 36 vis-à-visthe hole 60 bored through the bottom of the cabinet 12 as shown in FIG.5. The fan case 36 has another hole 37 formed along the side locatedclose to the heat sink 38 that is to be cooled by supplying cooling air.

The heat sink 38 is rigidly fitted to the third fitting surface 54. Theheat sink 38 typically has a corrugated profile or a fan-shaped profileand is made of a metal that performs well for emitting heat such asaluminum. The base 20 and the fan case 36 may be made of a metal thatperforms well for emitting heat such as aluminum or iron. The base 20 isprovided with fitting holes 70 at appropriate positions. Thus, the base20 is rigidly secured to the cabinet 12 as screws are driving into therespective bosses 72 arranged on the inner surface side of the cabinet12 by way of the respective holes 70.

As shown in FIGS. 5 and 6, the heat sink 38 is arranged at a positionvis-à-vis the hole 76 formed through a lateral wall of the cabinet 12.With this arrangement, as the motor 30 is driven, the fan 34continuously revolves in the sense as indicted by arrow R in FIG. 6 sothat air is driven out from the inside of the cabinet 12 to the outsidethrough the lateral hole 76 by way of the hole 60 and the hole 48 in thedirections indicated by arrows D1, D2 and D3. At this time, the heatgenerated by the heat emitting element 40 is transmitted to the fittingsurface 54 by way of the fitting surfaces 50, 52 of the base 20 so thatconsequently the heat is transmitted to the heat sink 38. As the airflow that is produced by the revolutions of the fan 34 takes place inthree directions indicated by the arrows D1, D2 and D3, the heattransmitted to the heat sink 38 is released to the outside by way of thelateral hole 76 of the cabinet.

FIG. 7 is a schematic cross sectional view of the motor 30 of FIG. 6.The motor 30 has a rotor 80 and a stator 84.

The motor 30 and the fan 34 are contained in the fan case 36 and thestator 84 is integrally arranged on the top section 36A of the fan case36. The stator 84 has a stator yoke 88, a bearing unit 90, a coil 164and a core 160.

The stator yoke 88 may be integral with the top section 36A of the fancase 36 or separated from the latter. It is typically made of iron orstainless steel. The housing 120 of the bearing unit 90 is rigidlysecured to the inside of the holder 92 by press fitting and/or adhesion.The holder 92 is a cylindrical part of the stator 84.

Roughly speaking, the bearing unit 90 has a shaft 100, a radial bearing130, a space-forming member 113, a holding member 120 and lubricatingoil 150.

FIG. 8 is an enlarged view of the bearing unit 90 shown in FIG. 7,illustrating its configuration.

Now, the structure of the bearing unit 90 will be described in greaterdetail by referring to FIG. 8.

The shaft 100 is a so-called I-shaped shaft, which is also referred toas straight type shaft. The shaft 100 is typically made of stainlesssteel. The shaft 100 has an exposed end section 160, an inner endsection 161 and a tapered section 100A. The exposed end section 160 andthe shaft outer peripheral section 162 may be made to have a samediameter. The tapered section 100A is a tapered part located between theexposed end section 160 and the shaft outer peripheral section 162. Thetapered section 100A is tapered from the shaft outer peripheral section162 toward the exposed end section 160. The exposed end section 160 is apart of the shaft 100 that extends from the gap S of the holding member120 so as to be exposed to the outside. The tapered section 100A isarranged at the position located vis-à-vis the gap S.

The radial bearing 130 illustrated in FIG. 8 is a cylindrical bearingthat may typically be made of sintered metal so as to operate ashydrodynamic fluid bearing. The radial bearing 130 has a pair of twodynamic pressure generating grooves 190, 190 formed on the innerperipheral surface thereof. The dynamic pressure generating grooves 190,190 are separated from each other by a predetermined distance. One ofthe dynamic pressure generating grooves 190, 190 is located near the gapS, while the other dynamic pressure generating groove 190 is located atthe side of the inner end section 161. For example, herring bone groovesmay be adopted for the dynamic pressure generating grooves 190, 190. Theradial bearing 130 rotatably and radially supports the shaft 100.

An anti-shaft-release member 115 is also illustrated in FIG. 8. Theanti-shaft-release member 115 may be made of a polymeric material suchas nylon or provided as an E-ring that is made of metal. Theanti-shaft-release member 115 is mechanically fitted into a fittingrecess 169 formed at the side of the inner end section 161 of the shaft100. The anti-shaft-release member 115 prevents the shaft 100 fromslipping out from the radial bearing 130 in the direction of E shown inFIG. 8 along the central axis CL of the shaft 100.

The space-forming member 113 shown in FIG. 8 is a member for securing aspace around the anti-shaft-release member 115. The space-forming member113 is arranged in the holding member 120. The space-forming member 113has a squirrel cage-shaped member showing a U-shaped cross sectionalview. The space-forming member 113 is typically made of a polymericmaterial such as nylon or a metal material such as brass.

The holding member 120 show in FIG. 8 is used to contain the radialbearing 130, the shaft 100, the anti-shaft-release member 115 and thespace-forming member 113 in a sealed and seamless state. The holdingmember 120 is also referred to as housing and has a sole gap S arrangedvis-à-vis the tapered section 100A. The holding member 120 is typicallymade of a polymeric material such as nylon, LCP (liquid crystal polymer)or Teflon (tradename).

Lubricating oil is filled into the space among the radial bearing 130,the shaft outer peripheral section 162 of the shaft 100, theanti-shaft-release member 113 and the space-forming member 113.

The bearing unit 90 shown in FIG. 8 is provided at a position near theexposed end 160 of the shaft 100 with a radially arranged gap S. Sincethe bearing unit 90 is completely covered by the holding member 120,which is a seamless member, except the gap S, lubricating oil would notleak to the outside of the holding member 120 and hence the bearing unit90 is highly reliable.

The bearing unit 90 is provided in the inside with an anti-shaft-releasemember 115 that prevents the shaft 100 from slipping away so that it iseasy to handle the motor that is equipped with the bearing unit 90.

The shaft 100 is provided with a tapered section 100A at a positionlocated vis-à-vis the gap S. The tapered section 100A and the gap Scooperate to form a surface tension seal. A surface tension sealoperates as a lubricating oil holding means that utilizes the capillaryphenomenon. In the case of the bearing unit 90, lubricating oil is drawntoward the side where that gap S is narrower, or toward the inside ofthe bearing unit 90 and hence would not leak to the outside. Theprinciple of such a surface tension seal lies in the provision of atapered section 100A to give rise to a pressure gradient there and drawthe lubricating oil there toward the inside of the bearing unit 90. Thetapered section 100A may be arranged either on the shaft 100 or on theholding member 120.

Now, the reason why an anti-shaft-release member 115 has to be providedwill be described below.

In the case of a motor 30 equipped with a bearing unit 90 according tothe invention and shown in FIG. 7, the rotor 80 would slip away when themotor 30 is subjected to impact unless the rotor 80 including the shaft100 is provided with some anti-release means. Therefore, it isabsolutely necessary to provide the rotor 80 with an anti-release meansin view of the anti-impact performance of the motor 30.

In the case of a spindle motor to be used as optical disc drive, it isalso necessary to provide some anti-release means in order to preventthe rotor 80 from slipping away when an optical disc is mounted ordismounted.

Conventionally, an anti-release member that is necessary for the rotorsection is arranged outside the bearing unit or, if it is arranged inthe inside of the bearing unit, the holding member of the bearing unitis made to have a plurality of components so that it may be assembledafter arranging the anti-release member in the inside of the bearingunit. However, the former arrangement is accompanied by the drawbackthat the motor inevitably has large outer dimensions and the operationof assembling the motor is a complex one. The latter arrangement, on theother hand, is accompanied by the drawback that the holding memberincludes a binding section and lubricating oil can easily leak throughit.

To the contrary, in a bearing unit 90 according to the invention, theanti-shaft-release member 115 is arranged in the inside of the bearingunit 90 and the holding member 120 is a seamless member. Thus, thebearing unit 90 can be easily mounted in the motor 30 and there is norisk for lubricating oil to leak out. Thus, a bearing unit 90 accordingto the invention is highly reliable and can enjoy a long service life.

FIGS. 9A through 9C are schematic cross sectional views of the bearingunit 90 of FIG. 8, showing assembling steps thereof.

Referring, firstly, to FIG. 9A, the shaft 100 to which theanti-shaft-release member 115 is fitted is inserted into the radialbearing 130.

Then, as shown in FIG. 9B, the space-forming member 113 is fitted to theradial bearing 130. Thereafter, as shown in FIG. 9C, the holding member120 is formed typically by outsert molding.

The lubricating oil is filled into the bearing unit 90 typically byvacuum impregnation and the volume of lubricating oil is regulated toproduce a complete bearing unit 90.

Due to the provision of the space-forming member 113, a gap is securedaround the anti-shaft-release member 115 and the shaft 100 is rotatablysupported with the anti-shaft-release member 115 if the holding member120 is formed from resin by outsert molding.

In the instance of FIG. 8, the inner bottom surface of the space-formingmember 113 also operates as thrust bearing for rotatably supporting theinner end section 161 of the shaft 100 in the thrusting direction. Thespace-forming member 113 rotatably supports the inner end section 161 aspivot.

A bearing unit according to the invention may alternatively have aconfiguration as shown in FIG. 10. The bearing unit 490 shown in FIG. 10comprises a shaft 400, an anti-shaft-release member 415, a radialbearing 430, a space-forming member 413 and a holding member 420.

Of the bearing unit 490 shown in FIG. 10, the disc-shapedanti-shaft-release member 415 is integrally formed with the inner endsection 461 of the shaft 400. In other words, the shaft 400 is formedwith the anti-shaft-release member 415 in such a way that thelongitudinal cross section thereof shows a substantially T-shapedprofile.

Dynamic pressure generating grooves 428 are formed on the oppositesurfaces of the anti-shaft-release member 415. The dynamic pressuregenerating grooves 428 generate dynamic pressure when theanti-shaft-release member 415 is rotatably supported in the space of thespace-forming member 413.

The space-forming member 413 is typically made of metal such as brass orstainless steel or resin such as LCP, polyamide or polyimide for thepurpose of accurately producing a gap around the anti-shaft-releasemember 415. The holding member 420 is typically made of resin such asLCP, nylon, polyamide, polyimide or Teflon (tradename). The holdingmember 420 is a seamless member except the gap S.

The above described anti-shaft-release member 415 operates to preventthe shaft 400 from slipping away from the radial bearing 430 in the Edirection shown in FIG. 10. However, the anti-shaft-release member 415takes not only the role of preventing the shaft 400 from slipping awaybut also the role of a hydrodynamic fluid bearing type thrust bearingmeans that is provided with dynamic pressure generating groove 428.

Dynamic pressure generating grooves 480 may be formed on the innerperipheral surface of the radial bearing 430. However, dynamic pressuregenerating grooves 480 may alternatively be formed on the outerperipheral surface 462 of the shaft 400 instead of the inner peripheralsurface of the radial bearing 430.

Dynamic pressure generating groove 428 may be formed not only on theopposite surfaces of the anti-shaft-release member 415 but also on theinner end section 431 of the radial bearing 430 and on the inner endsurface section 414 of the space-forming member 413.

The anti-shaft-release member 415 is typically made of stainless steeland may be formed completely integrally with the shaft 400 or preparedseparately from the shaft 400. While the shaft 400 is typically made ofstainless steel, it may alternatively be formed by outsert molding,using resin such as LCP, polyamide, polyimide or PC (polycarbonate).

The bearing unit 490 of FIG. 10 can easily adopt a hydrodynamic bearingstructure both radially and in the thrusting direction. Therefore, thebearing unit 490 of FIG. 10 can be more reliable and enjoy a longerservice life if compared with the bearing unit 90 of FIG. 8.

FIG. 11 is a schematic cross sectional view of still another embodimentof bearing unit according to the invention.

The bearing unit 590 of FIG. 11 has a configuration substantially sameas the bearing unit 490 of FIG. 10. Therefore, the components of thebearing unit 590 of FIG. 11 that are same as or similar to theircounterparts of the bearing unit 490 of FIG. 10 are denoted respectivelyby the same reference symbols and will not be described in detail.

The bearing unit 590 of FIG. 11 differs from the bearing unit 490 ofFIG. 10 in terms of the profile of the holding member 520, the role ofthe anti-shaft-release member 415 and that of the space-forming member413.

The holding member 520 has a gap S and another opening 530. Thespace-forming member 413 is exposed to the outside through the opening530.

The shaft 400 is typically made of an electrically conductive materialsuch as stainless steel. The space-forming member 413 is also typicallymade of an electrically conductive material such as stainless steel orbrass. As pointed out above, the space-forming member 413 is exposed tothe outside through the opening 530.

With this arrangement, the static electricity that is generated when themotor shown in FIG. 11 is driven to operate is released to outside andthen to the ground by way of the shaft 400, the anti-shaft-releasemember 415 and the space-forming member 413 as indicated by arrow E inFIG. 11.

Thus, when a bearing unit according to the invention is mounted in ahard disc drive, for instance, and static electricity is generated toshow a voltage of 30V, the generated static electricity is released tothe outside and then to the ground by way of the above described route.Therefore, it is possible to prevent a phenomenon that the magnetic headarranged in the hard disc drive is broken down by the staticelectricity.

In this case, lubricating oil is filled in the space among thespace-forming member 413, the anti-shaft-release member 415, the outerperipheral section 462 of the shaft 400 and the radial bearing 430. Ifthe lubricating oil filled in the space is electrically conductive, thedischarging performance thereof can be improved by the arrangement ofthis embodiment.

Any of the bearing units 90, 490, 590 shown respectively in FIGS. 8, 10and 11 can be applied not only to a fan motor 30 as shown FIG. 5 butalso to a mechanism for driving an information recording medium in aninformation recording/reproduction device such as a hard disc drive asdescribed above.

Since a bearing unit according to the invention is provided with aspace-forming member, the anti-shaft-release member can be arranged inthe inside of the bearing unit, which is compact, then, it is possibleto downsize a motor in which such a bearing unit is mounted.Additionally, since the shaft would not slip away in the assemblingoperation, it is easy to handle the bearing unit. Still additionally,since the holding member that is a seamless member contains all theremaining components of the bearing unit except the part of the shaftprojecting to the outside through a small gap formed in the holdingmember, the lubricating oil in the inside would not leak out. Thus, thebearing unit is highly reliable and can enjoy a long service life.

Furthermore, a motor or some other rotary drive in which a bearing unitaccording to the invention is mounted can be downsized and is made freefrom any anti-release member arranged outside the motor so that therotary drive can be manufactured at low cost with a reduced number ofmanufacturing steps.

Now, still other embodiments of bearing unit according to the inventionwill be described below by referring to FIGS. 12A through 13D.

Each of these embodiments, which are described below, is provided with aradial bearing means and a thrust bearing means as bearing means forsupporting a shaft or a rotary shaft. The thrust bearing means arrangedat an end section of the shaft may be of the pivot type or thehydrodynamic fluid bearing type.

FIG. 12A is a schematic cross sectional view of an embodiment of bearingunit that comprises a radial bearing means and a thrust bearing means.In this embodiment, the front end section of the shaft is processed toshow a spherical profile and the thrust bearing means is formed by amember made of a polymeric material to receive the front end section ofthe shaft.

The bearing unit 201 comprises a shaft 202 formed by a metal materialsuch as stainless steel or a resin material and showing a roundrod-shaped profile and a bearing means 203 for supporting the shaft 202.In other words, a radial bearing means 204 for receiving a radial loadand a thrust bearing means 205 for receiving a thrust load are providedas bearing means 203.

A sintered and oil-impregnated bearing or a hydrodynamic fluid bearingis used for the radial bearing means 204 that rotatably and radiallysupport the shaft 202. As an example, the use of a hydrodynamic fluidbearing will be described below. The bearing is made of sintered metal,which may be a copper type metal or a copper/iron type metal and dynamicpressure generating grooves are formed on it. Lubricating oil is heldthere by means of the porous structure that is specific to sinteredmetal. In this embodiment, so-called herring bone grooves having aV-shaped cross section are formed as dynamic pressure generatinggrooves. Two groups of dynamic pressure generating grooves 204 a, 204 a,. . . and 204 b, 204 b, . . . are formed on the inner periphery of thecylindrical radial bearing means 204 and running in the sense in whichthe shaft revolves to make the radial bearing means 204 operate ashydrodynamic fluid bearing. However, the dynamic pressure generatinggrooves may alternatively be formed on the peripheral surface of theshaft 202. For the purpose of the invention, not only a hydrodynamicfluid bearing but also a bearing of any of various different types suchas a metal bearing may be used.

An annular engaging groove 202 a is formed on the shaft 202 at aposition close to the front end thereof and engaged with an annularanti-release member 206. The anti-release member 206 is a part typicallymade of a polymeric material such as nylon (normal chain aliphaticpolyamide) or a part made of a metal material and having a form of anE-ring. It operates as stopper for preventing the shaft 202 from axiallymoving and slipping away when axial external force is applied to theshaft 202 due to vibrations or a pressure change.

A member (to be referred to as “space-forming member” hereinafter) 207made of a polymeric material such as nylon, polyimide or liquid crystalpolymer (LCP) or a metal material such as brass is arranged around theanti-release member 206. The space-forming member 207 is arranged toform a space around the anti-release member 206 in a predeterminedmanner by considering that the anti-release member 206 is rigidly fittedto the shaft 202 and revolves with the latter.

In this embodiment, the resin made space-forming member 207 is realizedin the form of a bottomed hollow cylinder having a recess 207 a, whilethe corresponding end of the shaft 202 is made to show a sphericalprofile so as to contact the flat bottom of the space-forming member 207at a point. As for the thrust bearing means 205 for supporting the shaft202 in the thrusting direction, a member for bearing the correspondingend of the shaft can be eliminated when the end of the shaft is made toshow a curved surface and brought into contact with the space-formingmember 207. In other words, the space-forming member 207 operates as abearing member. The profile of the space-forming member is not limitedto the above described one. Alternatively, a projection or a bearingsection may be integrally formed with the space-forming member andbrought into contact with the corresponding end of the shaft.

The space-forming member 207 of this embodiment is additionally providedwith a stepped section 207 b that operates as receiving recess to bepartly engaged with the radial bearing means 204. The reason forproviding the space-forming member 207 with a stepped section 207 b willbecome apparent hereinafter in the description of a method ofmanufacturing a bearing unit according to the invention.

A member 208 for sealing lubricating oil (to be referred to as “sealmember” hereinafter) is arranged around the shaft so as to produce aminute radial gap G between the inner peripheral surface 208 a thereofand the shaft 202 at a position near the exposed part of the shaft 202.The seal member 208 has a hollow cylindrical profile and is typicallymade of a polymeric material such as nylon or polytetrafluoroethylene ora metal material. The seal member 208 is provided with a stepped section208 b. The stepped section 208 b operates as receiving recess to bepartly engaged with the radial bearing means 204. The reason forproviding the seal member 208 with a stepped section 208 b will becomeapparent hereinafter in the description of a method of manufacturing abearing unit according to the invention. A part 209 of the lubricatingoil that is filled in the bearing unit is found in the gap G as seenfrom FIG. 12B. The seal member 208 is provided with recesses 208 c thatcorrespond to the respective projections formed on the corresponding endfacet of the radial bearing means 204 and is adapted to define the axialdirection of the radial bearing means 204.

The housing member or the holding member 210 is used to hold thespace-forming member 207, the seal member 208 and the radial bearingmeans 204 from the outer peripheral side of the bearing unit. It istypically made of a resin material, or a polymeric material such aspolyimide, polyamide, nylon or LCP. In this embodiment, the housingmember 210 takes the role of binding the radial bearing means 204, thespace-forming member 207 and the seal member 208 together seamlesslywithout any gap. Thus, it is possible to prevent lubricating oil fromleaking.

In this embodiment, a special arrangement is devised to preventlubricating oil from leaking from the part of the shaft 202 exposed tothe outside.

More specifically, as shown in FIG. 12B in an enlarged scale, a part 202c of the shaft 202 that is located close to the part thereof exposed tothe outside and adapted to form the gap G with the seal member 208 istapered. The diameter of the tapered part 202 c of the shaft 202increases as it comes close to the inside of the bearing unit or theradial bearing means 204 along the shaft 202.

Thus, since the gap G is formed between the tapered section 202 c whosediameter increases toward the inside of the bearing unit and the innerperipheral surface 208 a of the seal member 208 arranged vis-à-vis thetapered section 202 c, the gap is reduced as it comes close to theinside of the bearing unit. If the drawing pressure that is generated bythe capillary phenomenon is “p”, it is expressed by the formula of “p=2γcos θ/c” (where γ: the surface tension of lubricating oil, θ: thecontact angle of lubricating oil, c: gap). In other words, p isinversely proportional to the gap dimension c (p □ 1/c). Thus, thesmaller the gap dimension c, the larger the drawing pressure becomes sothat the lubricating oil 209 in the gap dimension c is drawn to theinside of the bearing unit because the gap dimension c becomes smalleras it comes close to the inside. Therefore, lubricating oil 209 wouldnot leak out. When the shaft has a constant diameter, the gap isdifferentiated when the shaft becomes eccentric relative to the openingof the holding member and lubricating oil is urged to move to an areawhere the gap is small. However, when the shaft is provided with atapered section 202 c, the gap is made to vary along the axial directionand an elliptic cross section of the gap that is inclined relative tothe shaft always shows areas with a same clearance so that lubricatingoil would be biased least if eccentricity takes place. Additionally, thecentrifugal force that is generated as the shaft is driven to revolveprovides a sealing effect that prevents lubricating oil from dispersingto the outside.

Lubricating oil will be prevented from leaking further when a surfaceactive agent is applied to the exposed part of the shaft 202 and thesurface of the seal member 208. The contact angle θ of the shaft andlubricating oil is increased when a surface active agent is applied tothe shaft. As a result, the drawing pressure p is reduced. As theexternal drawing pressure p is reduced, the internal drawing pressure pis raised relatively to prevent lubricating oil from leaking andotherwise moving.

Now, a method of manufacturing a bearing unit according to the inventionwill be described by referring to FIGS. 13A through 13D, whichillustrate different steps of the process of assembling a bearing unit201 according to the invention. The bearing unit manufacturing methodcomprises the following steps:

-   (1) a shaft insertion step;-   (2) a step of fitting a space-forming member and a seal member;-   (3) a housing member forming step; and-   (4) a step of filling lubricating oil and regulating the amount of    lubricating oil.

Firstly, in step (1) illustrated in FIG. 13A, a shaft 202 to which ananti-release member 206 is fitted is inserted into a radial bearingmeans 204. Then, in step (2) illustrated in FIG. 13B, a space-formingmember 207 and a seal member 208 are fitted to the radial bearing means204. More specifically, as the stepped section 207 b of thespace-forming member 207 and the stepped section 208 b of the sealmember 208 are respectively fitted to the outer peripheral edges of thecorresponding end sections of the radial bearing means 204, the relatedparts of the radial bearing means 204 are received respectively in thecorresponding recess of the space-forming member 207 and that of theseal member 208.

When the operation of this step is completed, the shaft 202 is alreadyin a state where it is rotatably supported by the bearing means 203.

Then, in step (3) illustrated in FIG. 13C, a housing member 210 isformed by outsert molding, using a polymeric material such as nylon.

Thereafter, in step (4) illustrated in FIG. 13D, lubricating oil isfilled in the inside of the bearing unit by vacuum impregnation and theamount of lubricating oil is regulated. For example, lubricating oil ispartly forced out and removed by thermal expansion below a predeterminedtemperature level.

In the bearing unit 201 that is prepared in the above described manner,the radial bearing means 204, the space-forming member 207 and the sealmember 208 are bound together as the seamless housing member 210 isformed by outsert molding so that no gap is left among these members andlubricating oil is completely prevented from leaking. It is no longernecessary to control the packing operation that is conventionallyrequired for the binding section of the related members so that theprocess management is simplified.

While the seal member 208 may be molded in step (2) shown in FIG. 13B,it is preferable to prepare the seal member 208 in advance and fit it tothe radial bearing means 204 when the gap between the seal member andthe shaft is small for the purpose of raising the accuracy of the gap.If, for example, the gap dimension c is made greater than the specifiedvalue beyond a tolerance, the drawing pressure p generated by thecapillary force becomes too small. In other words, the gap is subjectedto an upper limit. Therefore, when a large amount of lubricating oil isrequired, the axial length of the gap G needs to be increased. Then, atechnically difficult process may be required to prepare the metal moldbecause the part of the metal mold to be used for forming the gap Gcomes to have a thin and axially long profile. If the molding accuracyis not sufficient, the gap dimension can show large variances. To thecontrary, when the seal member is prepared before step (2) illustratedin FIG. 13B, it can show a satisfactory level of accuracy and hence thegap can also be produced accurately. Since the impact-resistance isinversely proportional to the square of the gap dimension c, lubricatingoil is prevented from dispersing by reducing the gap dimension and itsvariance. However, it should be noted here that, as the gap dimension isreduced, the level of the surface of lubricating oil can movesignificantly as the oil temperature rises and the lubricating oil inthe inside expands.

The space-forming member of the bearing unit may be made of a metalmaterial instead of a synthetic resin material as shown in FIG. 14.

The bearing unit 201A illustrated in FIG. 14 differs from theabove-described bearing unit 201 in a manner as described below. Notethat, in the following description, the components of the bearing unit201 A that are same as or similar to their counterparts of the bearingunit 201 are denoted respectively by the same reference symbols andwould not be described in detail.

In the bearing unit 201A illustrated in FIG. 14, the space-formingmember 207A is typically made of stainless steel, brass, a pressedmaterial or a sintered material and the thrust bearing means 205 has athrust bearing member 211 for receiving the corresponding shaft end 202b that is processed to show a spherical profile. The thrust bearingmember 211 is arranged in and fitted to a recess 207 a formed in thespace-forming member 207A. The thrust bearing member 211 is made of aresin material such as nylon, polyimide, polyamide or liquid crystalpolymer or a low friction material such as rubidium and formedseparately from the space-forming member 207A.

Since the space-forming member 207A of the bearing unit 201A is made ofmetal, a thrust bearing member 211 that is made of a resin material or alow friction material is provided in view of prolonging the service lifeof the bearing unit 201A. Thus, the requirements to be met in the stepof outsert molding of the housing member 210 that follows the step offitting the space-forming member 207A including the temperature and thepressure of injecting resin are alleviated by the arrangement of raisingthe rigidity and the resistance to high temperatures of thespace-forming member 207A. Differently stated, while the cost of thisembodiment of bearing unit can be raised due to the provision of thethrust bearing member 211, it is possible to reduce the overall costbecause no particular requirements are imposed for the selection ofresin material and the molding requirements are alleviated.

Now, still another embodiment of bearing unit according to the inventionwill be described by referring to FIG. 15. The bearing unit 201B of thisembodiment differs from the bearing unit 201 illustrated in FIG. 12A inthat the end section of the shaft shows a T-shaped profile in a lateralview and the thrust bearing means, which is a hydrodynamic fluidbearing, is formed by utilizing the anti-shaft-release member.Therefore, the components of the bearing unit 201B that are same as orsimilar to their counterparts of the bearing unit 201 are denotedrespectively by the same reference symbols and will not be described indetail.

Of the bearing unit 201B illustrated in FIG. 15, the anti-release member212 arranged at the front end of the shaft 202 has a disc-shaped profilewith a predetermined thickness and is made of a metal material such asbrass or stainless steel or a polymeric material such as nylon or LCP.The anti-release member 212 is provided on the opposite end facetsthereof including the facet 213 disposed vis-à-vis the radial bearingmeans 204 and the facet 214 disposed vis-à-vis the space-forming member207 with respective groups of dynamic pressure generating grooves 213 a,213 a, . . . and dynamic pressure generating grooves 214 a, 214 a, . . ..

The space-forming member 207 is additionally provided with a recess 207a for receiving the anti-release member 212 so that a space is formedaround the anti-release member 212. Lubricating oil is filled in the gapformed between the anti-release member 212 and the space-forming member207 and the gap formed between the anti-release member 212 and theradial bearing means 204.

Thus, the bearing unit 201B shows the configuration of a hydrodynamicfluid bearing realized by using the anti-release member 212 and thespace-forming member 207 for the thrust bearing means 205 and the shaft202 is rotatably supported relative to the hydrodynamic fluid bearing.Therefore, the bearing unit 201B is relatively free from vibrations andhence can suitably find applications to motors of recording devices suchas optical disc drives and hard disc drives.

While the manufacturing method comprising steps (1) through (4)described above by referring to FIGS. 13A through 13D can also be usedbasically for manufacturing the bearing unit 201B, it should be notedthat it is necessary to supply lubricating oil into the dynamic pressuregenerating grooves 213 a and 214 a and the space between the radialbearing means 204 and the space-forming member 207 in order to generatedynamic pressure to a predetermined level when the shaft is driven torevolve. How lubricating oil is supplied is defined by the dimensionalaccuracy of the anti-release member 212 and the space-forming member207.

While the dynamic pressure generating grooves 213 a, 214 a are formed inthe anti-release member 212 in this embodiment, the arrangement of thedynamic pressure generating grooves is not limited to the abovedescription and they may alternatively be formed on the surface of theradial bearing means 204 that is located vis-à-vis the anti-releasemember 212 or the surfaces of the space-forming member 207 locatedvis-à-vis the anti-release member 212.

Now, a rotary drive according to the invention will be described below.

FIG. 16 is an embodiment of a rotary drive comprising a bearing unit 201according to the invention that is applied to a fan motor. It may beappreciated that the bearing unit 201 may be replaced by a bearing unit201A or bearing unit 201B.

Referring to FIG. 16, the rotary drive 215 comprises a rotor section 216and a stator section 217 that includes the bearing unit 201.

The rotor section 216 that operates as rotary body (rotor) is providedwith a rotor yoke 218, a magnet 219, a plurality of blades 220, 220, . .. and an end of a shaft 202 that operates as a rotary shaft is rigidlypress-fitted and secured to the boss section 221 arranged at the centerof rotation of rotor section 216. The annular magnet (plastic magnet)219 that is magnetized along the periphery thereof is bonded and securedto the inner peripheral surface of the rotor yoke 218 and the pluralityof blades 220, 220 . . . is arranged peripherally on the outerperipheral surface of the cylindrical section 216 a of the rotor section216 at predetermined regular angular intervals.

The bearing unit 201 is arranged in the stator section 217 as a shaftsupporting means for rotatably supporting the shaft 202 that revolveswith the rotor section 216. More specifically, the bearing unit 201 isreceived in a recess 223 of a cylindrical support section 222 a that isformed in a stator yoke 222 of the stator section 217. It ispress-fitted or bonded to the recess 223. Coil sections 226, each ofwhich includes a core 224 and coil 225, are arranged at respectivepositions located vis-à-vis the inner peripheral surface of the magnet219 to form a rotary body drive means 227 along with the magnet 219 andthe rotor yoke 218.

The rotary drive 215 has a case 228, which is provided with a hole 228a. As the coil sections 226 are electrically energized to drive therotor section 216 to revolve, air flows in through the hole 228 a asindicated by arrow A in FIG. 16 and then expelled to the outside througha blast nozzle (not shown) formed in the case 228.

As a fan motor as described above mounts the bearing unit 201,lubricating oil would not leak out to improve reliability and prolongthe service life of the bearing unit 201. Additionally, when ahydrodynamic fluid bearing type radial bearing means 204 is used,lubricating oil is further prevented from leaking to realize a motorthat is highly reliable and adapted to revolve at a high rate.Therefore, such a bearing unit can suitably be used in a device as acooling fan that is required to show a high cooling performance. Forexample, a bearing unit according to the invention may find applicationsin cooling systems for cooling a heat emitting body such as a CPU of acomputer, where heat generated from the heat emitting body istransmitted to a heat sink and the heat sink is cooled by air blown by afan.

The posture of arrangement of the rotary drive 215 does not give rise toany problem in terms of the direction of the shaft 202. For example, therotary drive 215 may be arranged upside down relative to the postureshown in FIG. 16. In short, the rotary drive 215 is not subjected tosignificant restrictions in terms of positional arrangement.

A rotary drive according to the invention can find applicationsincluding not only fan motors but also motors of rotary drives ofdisc-shaped recording mediums and various other electric devices such asrotary head drums.

As described above, a bearing unit according to the invention is soconfigured that, after fitting a space-forming member, a seal member andother necessary members to the rotary shaft support means, which may bea radial bearing, the members are contained in and surrounded by ahousing member, which has a seamless structure and made of a polymericmaterial, without producing any gap in the inside. Therefore, thebearing unit is free from the problem of leakage of lubricating oil fromthe inside. Thus, the present invention provides a bearing unit that ishighly reliable and can enjoy a long service life.

Additionally, a bearing unit according to the invention is manufacturedby a simple manufacturing method that comprises only a reduced number ofsteps and it is not necessary to control the packing operation, using anadhesive agent, and the operation of checking the sealed condition ofthe bearing unit.

Still additionally, a bearing unit according to the invention ismanufactured highly reliably at low cost and can enjoy a long servicelife due to the use of a hydrodynamic fluid bearing made of sinteredmetal and a molded housing member made of resin.

Furthermore, a bearing unit according to the invention can provide anecessary level of accuracy even when the gap between the seal memberand the shaft is relatively small and reduce the deviation of the gap G.

Now, still other embodiments of bearing unit according to the inventionand those of rotary drive using a bearing unit according to theinvention will be described below by referring to the related drawings(FIG. 17).

The following embodiments will be described in terms of motors to beused for heat-emitting devices of electric apparatus such as portablecomputers, or information processing apparatus for processing variouskinds of information. A portable computer is provided in the insidethereof with a heat-emitting device. The heat-emitting device comprisesa metal made base, a motor 301 fitted to the base, a fan 303 driven torevolve by the motor 301, a fan case 304 containing the fan 303 in theinside and a heat sink. The motor 301 for driving the fan 303 of theheat-emitting device to revolve will be described in detail below.

The motor 301 that is provided with a bearing unit 330 according to theinvention comprises a rotor 311 and a stator 312 as shown in FIG. 17.

The stator 312 is arranged on and integrally formed with the upper plate304 a of the fan case 304, which contains the motor 301 and the fan 303that is driven to revolve by the motor 301. The stator 312 has a bearingunit 330 according to the invention, coils 314 and cores 315 aroundwhich the coils 314 are wound respectively. The stator yoke 313 may beintegrally formed with the upper surface section 304 a of the fan case304. In other words, they may be formed as part of the fan case 304 orseparately from the fan case 304. The stator yoke 313 is typically madeof iron. The bearing unit 330 is rigidly secured to the inside of thehollow cylindrical holder 316 that is formed at the center of the statoryoke 313 by press-fitting and/or bonding.

The holder 316 into which the bearing unit 330 is press-fitted is formedintegrally with the stator yoke 313 to show a hollow cylindricalprofile.

The cores 315, around which the respective coils 314 are wound, arefitted to the outer periphery of the holder 316 that is integral withthe stator yoke 313. A drive current is supplied to the coils 314.

The rotor 311 that forms the motor 301 along with the stator 312 isfitted to the rotary shaft 331 that is rotatably supported by thebearing unit 330 so that it revolves with the rotary shaft 331. Therotor 311 comprises a rotor yoke 317 and a fan 303 having a plurality ofblades 319 that revolve integrally with the rotor yoke 317. The blades319 of the fan 303 is integrally formed with the rotor yoke 317 on theouter peripheral surface of the rotor yoke by outsert molding.

A rotor magnet 320 is arranged on the inner peripheral surface of thecylindrical section 317 a of the rotor yoke 317 so as to face the coils314 of the stator 312. The magnet 320 is a plastic magnet that is somagnetized as to show S poles and N poles that are alternately andperipherally arranged and rigidly fitted to the inner peripheral surfaceof the rotor yoke 317 by means of an adhesive agent.

The rotor yoke 317 is made to revolve integrally with the rotary shaft331 as the fitting section 332 formed at the front end of the rotaryshaft 331 that is supported by the bearing unit 330 is press-fitted intothe boss section 321 of the plate section 317 b that is provided at thecenter thereof with a through hole 321 a.

As a drive current is supplied to the coils 314 of the stator 312 with apredetermined energizing pattern from a drive circuit section arrangedoutside relative to the motor 301, the rotor 311 of the motor 301 havingthe above described configuration is driven to revolve with the rotaryshaft 331 under the effect of the magnetic fields generated in therespective coils 314 and the magnetic field produced from the rotormagnet 320 of the rotor 311. As the rotor 311 revolves, the fan 303having a plurality of blades 319 and fitted to the rotor 311 alsorevolves with the rotor 311. As the fan 303 revolves, air is drawn infrom the outside of the computer device through the opening cut throughthe cabinet of the computer and made to flow into the cabinet so as topass through the heat sink arranged in the cabinet before it is expelledto the outside of the cabinet through a through hole also cut throughthe cabinet so that the heat generated by the heat emitting element isdischarged to the outside of the computer main body and cool thecomputer main body.

Now, the bearing unit 330 that is used in the motor 301 will bedescribed in greater detail below.

As shown in FIGS. 17, 18 and 19, the bearing unit 330 that rotatablysupports the rotary shaft 331 of the above described motor 301 comprisesa radial bearing 333 for peripherally supporting the rotary shaft 331, aspace-forming member 334 formed outside the radial bearing 333, ahousing 337 containing the space-forming member 334 and a communicationpassage way 350 formed between the space-forming member 334 and theradial bearing 333.

The radial bearing 333 is made of sintered metal and has a hollowcylindrical profile. The radial bearing 333 forms a hydrodynamic fluidbearing along with the lubricating oil 342 filled in the housing 337,which lubricating oil 342 is viscous fluid. Dynamic pressure generatinggrooves 343, 344 are formed on the inner peripheral surface of theradial bearing 333 for receiving the rotary shaft 331.

As shown in FIG. 20, the dynamic pressure generating grooves 343, 344include respective pairs of grooves 343 a, 344 a that are formed on theinner peripheral surface of the radial bearing 333 so as to showV-shapes and linked together respectively by link grooves 343 b, 344 bthat run peripherally. The dynamic pressure generating grooves 343, 344are arranged in such a way that the front ends of the pairs of grooves343 a, 344 a that show V-shapes are directed in the direction ofrevolution R1 of the rotary shaft 331. In this embodiment, the dynamicpressure generating grooves 343, 344 are arranged in parallel with eachother and one above the other in the axial direction of the cylindricalradial bearing 333, of which the dynamic pressure generating grooves 343are located at the open side of the shaft, or close to the exposed partof the shaft, while the dynamic pressure generating grooves 344 arelocated at the closed side of the shaft or close to thrust bearing,which will be described hereinafter. The number and the size of thedynamic pressure generating grooves 343 and those of the dynamicpressure generating grooves 344 may be selected appropriately dependingon the size and the length of the radial bearing 333. The radial bearing333 may be made of brass, stainless steel or a polymeric material.

As the rotary shaft 331 inserted into the radial bearing 333, which isformed as hydrodynamic fluid bearing, is driven to revolve continuouslyaround the central axis CL in the direction of R1 in FIG. 20, thelubricating oil 342 filled in the housing 337 flows through the dynamicpressure generating grooves 343, 344 to generate dynamic pressurebetween the outer peripheral surface of the rotary shaft 331 and theinner peripheral surface of the radial bearing 333 to support therevolving rotary shaft 331. The dynamic pressure that is generated atthis time minimizes the coefficient of friction between the rotary shaft331 and the radial bearing 333 to make the rotary shaft 331 revolve verysmoothly.

Meanwhile, in the bearing unit 330, the width of the dynamic pressuregenerating grooves 344 as viewed in the thrusting direction is madegreater than the width of the dynamic pressure generating grooves 343 asviewed in the thrusting direction. With this arrangement, the dynamicpressure P343 generated in the dynamic pressure generating grooves 343at the open end side of the shaft and the dynamic pressure P344generated in the dynamic pressure generating grooves 344 at the closedend side of the shaft show a relationship of P343<P344.

The dynamic pressure P344 at the closed end side of the shaft is madegreater than the dynamic pressure P343 at the open end side of the shaftfor the reason as described below. The generation of the dynamicpressure simultaneously generates change in static pressure. If thedynamic pressure P343 and the dynamic pressure P344 are made to show arelationship of P343>P344 that is inverted from the above relationship,or if the dynamic pressure at the open end side of the shaft is madegreater than the dynamic pressure at the closed end side of the shaft,the distribution of static pressure is inverted relative to that ofdynamic pressure. Then, the static pressure becomes higher at the closedand sealed end side of the shaft than at the open end side of the shaft.Then, the static pressure that is generated simultaneously with therevolutions of the shaft gives rise to a phenomenon of pushing up theshaft, or a floating shaft phenomenon.

In the bearing unit 330, the width of the dynamic pressure generatinggrooves 343 is made greater than the width of the dynamic pressuregenerating grooves 344 to establish a relationship of P343<P344 betweenthe dynamic pressure P343 at the open end side of the shaft and thedynamic pressure P344 at the closed end side of the shaft in order toprevent a floating shaft phenomenon from taking place and make thestatic pressure at the open end side of the shaft greater than thestatic pressure at the closed end side of the shaft. In other words, theshaft is drawn toward the closed end side, or toward the side of thethrust bearing, which will be described hereinafter.

The space-forming member 334 that is arranged outside the radial bearing333 shows a profile adapted to contain and surround the radial bearing333, which is formed to show a cylindrical profile and is typically madeof synthetic resin.

As shown in FIGS. 18 and 21, the space-forming member 334 includes aspace-forming member main body 335 formed to surround the lateralsurface and the bottom surface of the radial bearing and a space-formingmember lid section 336 formed to cover the top surface of the radialbearing. The space-forming member lid section 336 is provided at thecenter thereof with a shaft receiving through hole 336 a that allows therotary shaft 331, which is rotatably supported by the radial bearing333, to run through it.

A thrust bearing 346 is integrally formed with the space-forming membermain body 335 at the center of the inner surface of the bottom thereof.The thrust bearing 346 is adapted to rotatably support the bearingsupport section 331 a of the rotary shaft 331 that is arranged at theclosed end of the rotary shaft 331 supported by the radial bearing 333as viewed in the thrusting direction. The space-forming member 334 ismade of synthetic resin and hence the thrust bearing 346 that isintegral with the space-forming member 334 is also made of syntheticresin. The thrust bearing 346 is formed as a pivot bearing that supportsthe bearing support section 331 a of the rotary shaft 331 that is madeto show a curved or tapered profile at a point.

Claw-like restricting sections 335 a are formed at upper parts of thespace-forming member main body 335. The claw-like restricting sections335 a are arranged along a circle so as to rigidly secure thespace-forming member lid section 336 and make the latter cover the topsurface of the radial bearing. Additionally, the space-forming membermain body 335 is provided at the lateral wall thereof with openings 335b that allow the outer peripheral surface of the radial bearing to beexposed to the outside when the radial bearing is contained in thespace-forming member 334.

While the space-forming member 334 is made of synthetic resin in theabove description, it may alternatively be made of metal or acombination of synthetic resin and metal. It is not subjected to anyparticular limitations in terms of material. When the space-formingmember 334 is made of synthetic resin, it is possible to design it in aningenious way particularly in terms of phase index relative to theradial bearing and manufacture it at low cost. Examples of resinmaterials that can be used to form the space-forming member 334 includefluorine type synthetic resin materials such as polyimide, polyamide andpolyacetal, polytetrafluoroethylene Teflon (tradename), nylon, PC(polycarbonate), ABS (acrylonitrilbutadienestyrene) and other syntheticresin materials.

A communication passage way 350 is formed between the space-formingmember 334 and the radial bearing 333. The communication passage way 350makes the end of the shaft projecting out from the radial bearing 333 inthe thrusting direction and the other end of the shaft communicate witheach other. In other words, the communication passage way 350 allows theend of the shaft where the thrust bearing 346 is formed and the otherend of the shaft that is located at the side of the shaft receivingthrough hole 336 a of the space-forming member lid section 336communicate with each other.

As shown in FIGS. 21 and 22, the communication passage way 350 includesa first groove 351 formed on the outer peripheral surface of the radialbearing 333 so as to run in the thrusting direction, a second groove 352formed on the end facet of the radial bearing 333 located close to thethrust bearing 346 and a third groove 353 formed on the opposite endfacet of the radial bearing 333.

The communication passage way may alternatively be arranged at the sideof the space-forming member 334 as shown in FIGS. 23 and 24. Morespecifically, when the communication passage way 360 is arranged at theside of the space-forming member 334, it comprises a first groove 361formed on the inner peripheral surface of the space-forming member mainbody 335 of the space-forming member 334 in the thrusting direction, asecond groove 362 formed on the inner surface of the bottom section ofthe space-forming member main body 335 and a third groove 363 formed onthe inner surface of the space-forming member lid section 336. Stillalternatively, the first through third grooves 351 through 353 arrangedat the radial bearing side and the first through third grooves 361through 363 arranged on the space-forming member 334 may be combined.

As pointed out above, in the bearing unit 330 of this embodiment, thewidth of the dynamic pressure generating grooves 344 is greater thanthat of the dynamic pressure generating grooves 343 and the dynamicpressure P344 at the closed side of the shaft is greater than thedynamic pressure P343 at the open side of the shaft. While thisarrangement can suppress the floating shaft phenomenon that is producedby the revolving shaft, the residual air can be expanded at the closedend of the shaft due to the reduction of the static pressure at thisside to give rise to a phenomenon that expanded air forces outlubricating oil.

However, the communication passage way 350 or the communication passageway 360 prevents lubricating oil from being forced out by the airremaining in the housing and/or the air dissolved in the lubricating oilbecause the open side end of the rotary shaft 331 that is projectingfrom the radial bearing 333 and the closed side end of the shaft 331communicate with each other so that the static pressure at the closedside end of the rotary shaft 331 does not fall. In other words, thecommunication passage ways 350, 360 can short circuit the pressurizedair at the opposite ends of the dynamic pressure generating grooves 343,344 arranged on the radial bearing 333 so that no pressure differenceoccurs and hence the floating shaft phenomenon does not appear.

As shown in FIG. 19, the housing 337 that contains the space-formingmember 334 has a profile adapted to surround and contain thesubstantially cylindrical space-forming member 334. It is an integralmember formed by molding synthetic resin.

Referring to FIG. 19, the housing 337 includes a hollow cylindricalhousing main body 338, a bottom closure section 339 formed integrallywith the housing main body 338 and adapted to close one of the oppositeends of the housing main body 338 and a top closure section 340 formedintegrally with the housing main body 338 and adapted to close the otherend of the housing main body 338. A shaft receiving hole 341 is boredthrough the center of the upper closure section 340 so as to allow therotary shaft 331 that is housed in the housing 337 and rotatablysupported by the radial bearing 333 to pass through it.

The housing 337 having the above described configuration is formed byoutsert molding of a synthetic resin material to contain the cylindricalspace-forming member 334 therein so that the space-forming member 334 isformed integrally with and arranged in the housing main body 338.

Since the outer peripheral surface of the radial bearing 333 is partlyexposed to the outside through the opening 335 b of the space-formingmember main body 335, the radial bearing 333 is also made integral withthe housing 337 that is formed by outsert molding.

While the synthetic resin material of the housing 337 is not subjectedto particular limitations, a material can provide a large contact anglerelative to the lubricating oil 342 filled in the housing 337 so that itmay repel the lubricating oil 342. Since the space-forming member 334 isintegrally formed with the housing 337, the housing 337 is preferablymade of a synthetic resin material that shows an excellent lubricatingperformance. Examples of synthetic resin materials that can preferablybe used for the housing 337 include fluorine type synthetic resinmaterials such as polyimide, polyamide and polyacetal; althoughpolytetrafluoroethylene Teflon (tradename), nylon, PC (polycarbonate),ABS (acrylonitrilbutadienestyrene) and other synthetic resin materialsmay also be used. Alternatively, the housing 337 may be formed from aliquid crystal polymer that can be highly accurately molded. The housing337 that is molded from a liquid crystal polymer is highlyabrasion-resistant and shows an excellent lubricating performance.

Meanwhile, the bearing unit 330 of this embodiment is a so-called shaftopposite ends open type bearing unit in which the opposite ends of theshaft 331, one of which is projecting from the radial bearing 333,communicate with each other by way of the communication passage way 350.Conventional shaft opposite ends open type bearing units are accompaniedby the problem that lubricating oil can easily disperse when subjectedto impact. However, in the bearing unit 330 of this embodiment, thehousing 337 is made to be a seamless structure that is hermeticallysealed except around the shaft receiving hole 336 a and contains theradial bearing 333 and the space-forming member 334 in the inside sothat, while the open side end of the shaft that projects from the radialbearing and the closed side end of the shaft are made to communicatewith each other by way of the communication passage way 350, the bearingunit 330 is hermetically sealed and isolated from the outside exceptaround the shaft receiving hole 336 a arranged at the housing 337.Differently stated, since the communication passage way 350 is arrangedin the housing that is a seamless structure and hermetically sealedagainst the outside, lubricating oil is prevented from dispersing if itis subjected to impact.

The rotary shaft 33 1 that is rotatably supported by the thrust bearing346, which is integral with the radial bearing 333 arranged in theinside of the housing 337 and the housing 337, has at an end thereof thebearing support section 331 a of the shaft main body 331 b that shows acurved or tapered profile and is adapted to be supported by the thrustbearing 346 and the fitting section 332 at the other end thereof, towhich typically the rotor 331 of a motor 312, or a rotary body, isfitted. The fitting section 332 has a diameter the same as that of theshaft main body 331 b.

Referring to FIG. 19, the rotary shaft 331 is supported at the bearingsupport section 331 a thereof located at an end thereof by the thrustbearing 346 and at the outer peripheral surface of the shaft main body331 b by the radial bearing 333, while it is supported at the fittingsection 332 located at the opposite end thereof by the housing 337 withthe shaft projecting through the shaft receiving hole 341 arranged atthe top closure section 340 of the housing main body 338.

The rotary shaft 331 is provided with an anti-shaft-release groove 331 cthat is arranged between the bearing support section 331 a and the shaftmain body 331 b. On the other hand, the space-forming member 334 isprovided with a washer 349 that is arranged at a position correspondingto the anti-shaft-release groove 331 c and adapted to operate as ananti-shaft-release means. Thus, the operation of assembling the bearingunit can be handled with ease as the anti-shaft-release groove 331 c andthe washer 349 are brought into mutual engagement. The washer 349 maytypically be made of a polymeric material such as nylon, polyamide orpolyimide or a metal material such as stainless steel or phosphorbronze.

Meanwhile, the shaft receiving hole 341 is formed to have an innerdiameter slightly larger than the outer diameter of the shaft main body331 b so that the rotary shaft 331 that is made to run through the shaftreceiving hole 341 revolves without touching the inner peripheralsurface of the shaft receiving hole 341. The shaft receiving hole 341 isformed so as to provide a gap 345 with a gap dimension c that issufficient for preventing the lubricating oil 342 filled in the housing337 from leaking out of the housing 337 between the inner peripheralsurface of the shaft receiving hole 341 and the outer peripheral surfaceof the shaft main body 331 b. Thus, the top closure section 340, throughwhich the shaft receiving hole 341 is formed to produce a gap 345between the rotary shaft 331 and the shaft receiving hole 341 thatprevents the lubricating oil 342 filled in the housing 337 from leaking,operates as oil seal section.

Since the top closure section 340 that is integrally formed with thehousing 337 is made of synthetic resin such as polyimide, polyamide ornylon, it can secure a contact angle of about 60° for the innerperipheral surface of the shaft receiving hole 341 relative tolubricating oil 342. The bearing unit 330 of this embodiment can providethe top closure section 340 with a large contact angle relative tolubricating oil 342 without applying a surface active agent to the topclosure section 340 that operates as oil seal section and includes theinner peripheral surface of the shaft receiving hole 341. Therefore, thebearing unit 330 can prevent lubricating oil 342 from being driven tothe outside of the housing 337 through the shaft receiving hole 341 bythe centrifugal force generated when the rotary shaft 331 is driven torevolve.

Additionally, the part of the outer peripheral surface of the rotaryshaft 331 that is located vis-à-vis the inner peripheral surface of theshaft receiving hole 341 is provided with a tapered section 347. Thetapered section 347 is so inclined that the gap 345 formed between theouter peripheral surface of the rotary shaft 331 and the innerperipheral surface of the shaft receiving hole 341 expands as it comesclose to the outside of the housing 337. The tapered section 347produces a pressure gradient in the gap 345 between the outer peripheralsurface of the rotary shaft 331 and the inner peripheral surface of theshaft receiving hole 341 to generate force that tends to draw thelubricating oil 342 filled in the housing 337 toward the inside of thehousing 337. Thus, the lubricating oil 342 tends to be drawn to theinside of the housing 337 when the rotary shaft 331 is driven to revolveso that lubricating oil 342 reliably gets into the dynamic pressuregenerating grooves 358 of the radial bearing 333 that operates ashydrodynamic fluid bearing to reliably support the rotary shaft 331 andprevent the lubricating oil 342 filled in the housing 337 from leaking.

In the bearing unit 330 of this embodiment, the lubricating oil 342,which gets into the dynamic pressure generating grooves 358 arranged onthe radial bearing 333 that operates as hydrodynamic fluid bearing togenerate dynamic pressure, is filled in the bearing unit 330 in such away that that it fills the space from the inside of the housing 337 tothe gap 345 formed between the tapered section 347 of the rotary shaft331 and the inner peripheral surface of the shaft receiving hole 341. Inother words, the lubricating oil 342 is filled in all the gaps in thehousing 337 and impregnated into the radial bearing 333 that is made ofsintered metal.

Now the gap 345 formed between the tapered section 347 of the rotaryshaft 331 and the inner peripheral surface of the shaft receiving hole341 will be discussed. The minimum dimension of the gap 345 correspondsto the distance c between the outer peripheral surface of the rotaryshaft 331 and the inner peripheral surface of the shaft receiving hole341 and the dimension c is preferably between 20 μm and 200 μm, morepreferably about 100 μm. If the dimension c is smaller than 20 μm, it isdifficult to secure the necessary molding accuracy when integrallymolding the housing 337 of the bearing unit 330 from synthetic resin.If, on the other hand, the dimension c of the gap 345 is larger than 200μm, the impact-resistance of the lubricating oil 342 filled in thehousing 337 is reduced and lubricating oil outside of the housing 337when the bearing unit 330 is subjected to impact.

The impact-resistance G of the lubricating oil 342 filled in the housing337 that prevents lubricating oil from dispersing to the outside of thehousing 337 when the bearing unit 330 is subjected to impact isexpressed by formula (1) below;G=(12γ cos β/2pc2)/g   (1),where

-   -   γ: surface tension of lubricating oil,    -   β: contact angle of lubricating oil,    -   p: density of lubricating oil,    -   c: dimension of the gap between the rotary shaft and the shaft        receiving hole, and    -   g: free fall acceleration.

From the formula (1), it will be appreciated that the impact-resistanceG is inversely proportional to a square of the dimension c of the gap345.

The rise h of the oil surface due to thermal expansion is expressed byformula (2) below;h=VαΔt/2πRc   (2),where

-   -   V: volume of the filled lubricating oil,    -   α: thermal expansion coefficient,    -   Δt: temperature change, and    -   R: shaft half diameter.

From the formula (2), it will be appreciated that the rise h of the oilsurface is inversely proportional to the dimension c so that theimpact-resistance G rises when the dimension c is reduced but the rise hof surface of the filled lubricating oil 342 due to a temperature riseis extreme so that the axial length, or the height, of the shaftreceiving hole 341 needs to be increased to avoid problems.

As a result of an computing operation, it was found that theimpact-resistance is not smaller than 1,0000 G in a bearing unit 330having a rotary shaft 331 whose shaft diameter is between 2 mm and 3 mmwhen the dimension c of the gap 345 formed between the rotary shaft 331and the shaft receiving hole 341 is about 100 μm, while the height H1 ofthe shaft receiving hole 341, or the thickness of the top closuresection 340 of the housing 337, is about 1 mm. In this case, thelubricating oil 342 can withstand a high temperature level of 80° C. andthe bearing unit 330 can operate reliably so as to prevent thelubricating oil 342 filled in the housing 337 from dispersing.

Additionally, in the bearing unit 330 of this embodiment, the rotaryshaft 331 is provided with a tapered section 347 that is adapted toincrease the dimension c of the gap 345 formed between the outerperipheral surface of the rotary shaft 331 and the inner peripheralsurface of the shaft receiving hole 341 toward the outside of thehousing 337 so that a pressure gradient is formed in the gap 345 withthe dimension c formed between the outer peripheral surface of therotary shaft 331 and the inner peripheral surface of the shaft receivinghole 341 to draw the lubricating oil 342 filled in the housing 337toward the inside of the housing 337 by the centrifugal force that isgenerated when the rotary shaft 331 is driven to revolve.

Thus, in the bearing unit 330 of this embodiment, the gap 345 formedbetween the outer peripheral surface of the rotary shaft 331 and theinner peripheral surface of the shaft receiving hole 341 preventslubricating oil 342 from dispersing by effect of the surface tensionseal produced there.

Now, the surface tension seal will be described below. A surface tensionseal represents a sealing technique that utilizes the capillaryphenomenon of fluid. In the case of a capillary as shown in FIG. 26, therise h of the surface level of the liquid is determined by formula (3)shown below;2πrγ cos θ=mg   (3),where m is expressed by formula (4) below;m=πr2hp   (4),where

-   -   m: fluid mass within the range of h in the capillary,    -   r: half diameter of the capillary,    -   γ: surface tension of viscous fluid,    -   θ: contact angle of viscous fluid,    -   p: density of viscous fluid, and    -   g: gravity acceleration.

Formula (5) below is drawn from the formulas (3) and (4);h=2γ cos θ/rpg   (5).

Generally, the relationship between pressure P and the height of fluidis expressed by formula (6) below;P=pgh   (6).

Thus, formula (7) below is obtained from the formulas (5) and (6);P=2γ cos θ/r   (7).

In the formula (7), pressure P refers to the pressure that draws fluid.From the formula (7), the drawing pressure is greater when the diameterof the capillary is smaller.

While the above description is applied to a situation where thecapillary shows a circular cross sectional view, the lubricating oil 342that gets into the gap 345 formed between the outer peripheral surfaceof the rotary shaft 331 and the inner peripheral surface of the shaftreceiving hole 341 of the bearing unit 330 of this embodiment shows anannular cross sectional view as shown in FIG. 27. In this case, the riseh1 of the surface level of liquid, which is lubricating oil 342, isdetermined by formula (8) below;2π(R+r)γ cos θ=mg   (8),where m is expressed by formula (9) below;m=π(R2·r2)hp   (9)

Thus, formula (10) below is obtained from the formulas (8) and (9);h1=(2γ cos θ)/((R·r)pg)   (10).

If (R·r) is equal to the dimension c of the gap 345 that is formedbetween the outer peripheral surface of the rotary shaft 331 and theinner peripheral surface of the shaft receiving hole 341, formula (11)is obtained by transcribing the formula (10);h=(2γ cos θ)/(cpg)   (11).

Thus, when the lubricating oil 342 in the gap 345 shows an annular crosssectional view, the drawing pressure is expressed by formula (12) below;P=2γ cos θ/c   (12).

Now, a specific example of computing operation will be shown below.

If the dimension c of the gap 345 formed between the outer peripheralsurface of the rotary shaft 331 and the inner peripheral surface of theshaft receiving hole 341 is 0.02 cm (0.2 mm), the surface tension γ ofviscous fluid is 30 dyn/cm2 and the contact angle θ of lubricating oil342 is 15°, the drawing pressure is 2.86×10·3 atm from the formula (13).P=2×30×cos 15°/0.02=3.00×103dyn/cm2=2.86×10·3atm   (13).

From the formula (12), it will be seen that the drawing pressure P isgreater when the dimension c of the gap 345 is smaller. Thus, it will beseen that, when the rotary shaft 331 is provided with a tapered section347, the lubricating oil 342, which is viscous fluid, is drawn towardthe side where the dimension c of the gap 345 is smaller and hencetoward the inside of the housing 337.

For example, referring to FIG. 28, the drawing pressure P1 at positiont1 and the drawing pressure P2 at position t2 of the tapered section 347of the rotary shaft 331, the diameter at position t1 being differentfrom the diameter at position t2, show a relationship of P1>P2 from theformula (12) because the dimension c1 of the gap between the outerperipheral surface of the rotary shaft 331 and the inner peripheralsurface of the shaft receiving hole 341 and the dimension c2 of the gapbetween the outer peripheral surface of the rotary shaft 331 and theinner peripheral surface of the shaft receiving hole 341 have therelationship of c1<c2. Thus, it will be seen that the drawing pressure Ptrying to draw the lubricating oil 342 into the inside of the housing337 is greater when the dimension c of the gap 345 formed between theouter peripheral surface of the rotary shaft 331 and the innerperipheral surface of the shaft receiving hole 341 is smaller.

As the rotary shaft 331 is provided with a tapered section 347 thatmakes the dimension c of the gap 345 formed between the outer peripheralsurface of the rotary shaft 331 and the inner peripheral surface of theshaft receiving hole 341 decrease toward the inside of the housing 337so as to form a seal section for preventing the lubricating oil 342filled in the housing 337 from leaking to the outside of the housing337, a pressure gradient is produced in the lubricating oil 342 that isfound in the gap 345 formed between the outer peripheral surface of therotary shaft 331 and the inner peripheral surface of the shaft receivinghole 341. Thus, the pressure gradient of the lubricating oil 342 is suchthat the pressure trying to draw the lubricating oil 342 into the insideof the housing 337 increases as a function of the dimension c of the gap345. As a result of producing such a pressure gradient in thelubricating oil 342, the lubricating oil 342 is constantly subjected topressure P trying to draw it into the inside of the housing 337 so thatair is not drawn into the lubricating oil 342 in the gap 345 when therotary shaft 331 is driven to revolve.

When the above described tapered section 347 is not provided, or whenthe dimension c of the gap 345 between the outer peripheral surface ofthe rotary shaft 331 and the inner peripheral surface of the shaftreceiving hole 341 has a constant value along the longitudinal directionof the shaft receiving hole 341 as shown in FIG. 27, no pressuregradient is produced in the lubricating oil 342 that gets into the gap345 between the outer peripheral surface of the rotary shaft 331 and theinner peripheral surface of the shaft receiving hole 341 so thatlubricating oil 342 is found uniformly in the gap 345. Then, when therotary shaft 331 is driven to revolve, the lubricating oil 342 that getsinto the gap 345, which operates as seal section if its dimension cbetween the outer peripheral surface of the rotary shaft 331 and theinner peripheral surface of the shaft receiving hole 341 is decreasedtoward the inside of the housing 337, moves in the gap 345 so that itcan draw air E into itself. As air E is drawn into the lubricating oil342, the air E in the lubricating oil 342 expands when the temperatureand/or the pressure change to make lubricating oil 342 disperse from thegap 345, which operates as seal section, to the outside of the housing337.

To the contrary, in the bearing unit 330 of this embodiment, the rotaryshaft 331 is provided with a tapered section 347 that decreases thedimension c of the gap 345 between the outer peripheral surface of therotary shaft 331 and the inner peripheral surface of the shaft receivinghole 341 toward the inside of the housing 337 so that a pressuregradient is produced in the lubricating oil 342 that gets into the gap345 that makes the pressure being applied to the lubricating oil 342increase toward the inside of the housing 337. Therefore, air E isprevented from being drawn into the lubricating oil 342 when the rotaryshaft 331 is driven to revolve.

As a result of providing a tapered section 347 in a manner as describedabove, the lubricating oil 342 that gets into the gap 345 formed betweenthe outer peripheral surface of the rotary shaft 331 and the innerperipheral surface of the shaft receiving hole 341 is prevented fromdispersing to the outside of the housing 337 when the rotary shaft 331becomes eccentric relative to the shaft receiving hole 341 of thehousing 337 and additionally, lubricating oil 342 is allowed to get intothe gap 345 around the entire periphery of the rotary shaft 331 toprevent the rotary shaft 331 from being short of lubricating oil 342 andguarantee that the rotary shaft 331 revolves stably.

If the rotary shaft 331 is not provided with a tapered section 347 in amanner as described above and the rotary shaft 331 becomes eccentricrelative to the shaft receiving hole 341 of the housing 337, lubricatingoil 342 is concentrated to an area where the dimension c of the gapbetween the outer peripheral surface of the rotary shaft 331 and theinner peripheral surface of the shaft receiving hole 341 is small, whilelubricating oil 342 becomes scarce in the remaining area where thedimension c is large so that it draws air E into itself as shown in FIG.30. As air E is drawn into the lubricating oil 342, the air E in thelubricating oil 342 expands when the temperature and/or the pressurechange to make lubricating oil 342 disperse from the gap 345, whichoperates as a seal section, to the outside of the housing 337.

To the contrary, the rotary shaft 331 of the bearing unit 330 of thisembodiment is provided with a tapered section 347 so that, if the rotaryshaft 331 becomes eccentric relative to the shaft receiving hole 341 ofthe housing 337, the elliptic trajectory of the eccentric rotary shaft331 always shows areas with a same dimension c of the gap 345 as shownin FIG. 31. Then, the dimension c of the gap 345 formed between theouter peripheral surface of the rotary shaft 331 and the innerperipheral surface of the shaft receiving hole 341 on the elliptictrajectory shows a constant value along all the circumference of therotary shaft 331 as shown in FIG. 32 so that lubricating oil 342 wouldnot be concentrated to an area where the dimension c is small. Thus,lubricating oil 342 is prevented from dispersing from the gap 345 andhence from the inside of the housing 337.

While the rotary shaft 331 is provided with a tapered section 347 in theabove described bearing unit 330, alternatively the shaft receiving hole341 of the housing 337 may be provided with a tapered section 348 on theinner peripheral surface thereof as shown in FIG. 33.

Now, a process of manufacturing a bearing unit 330 according to theinvention and having the above described configuration will be describedbelow.

When manufacturing a bearing unit 330 according to the invention, it istemporarily assembled by fitting a space-forming member 334 to theoutside of a radial bearing 333. In this step of temporarily assemblinga radial bearing 333 and a space-forming member 334, a washer 349, whichis an anti-shaft-release means to be inserted into theanti-shaft-release groove 331 c formed between the bearing supportsection 331 a and the shaft main body 331 b of the rotary shaft 331, isfitted to the space-forming member main body 335 as shown in FIG. 34.Then, the space-forming member main body 335 and the space-formingmember lid section 336 are fitted to the radial bearing 333, which is ahydrodynamic fluid bearing. Note that a thrust bearing 346 is integrallyformed with the space-forming member main body 335 in the inside of thelatter. Additionally, a communication passage way 350 is formed betweenthe space-forming member 334 and the radial bearing 333.

Then, the radial bearing 333 and the space-forming member 334 that aretemporarily assembled are fitted to a metal mold and a housing 337 isformed around the outer periphery of the temporarily assembled radialbearing 333 and the space-forming member 334 by outsert molding of asynthetic resin material selected from the materials listed earlier asshown in FIG. 35. When the housing 337 is formed by outsert molding, thespace-forming member 334 is integrally arranged in the inside of thehousing 337 and pinched between the top closure section 340 and thebottom closure section 339 that are formed integrally with thecylindrical housing main body 338 so that its position is secured.Additionally, when the housing 337 is formed by outsert molding, theradial bearing 333 is integrally formed with the housing 337 by theopening 335 b of the space-forming member 334 and pinched between thetop closure section 340 and the bottom closure section 339 that areformed integrally with the cylindrical housing main body 338 so that itsposition is secured. Since the communication passage way 350 between thespace-forming member 334 and the radial bearing 333 is closed by thespace-forming member 334 when the housing 337 is formed by outsertmolding so that synthetic resin would not flow into it.

Then, the rotary shaft 331 is driven into the housing 337 through theshaft receiving hole 341 arranged in the top closure section 340 asshown in FIG. 36. At this time, the washer 349 that is ananti-shaft-release means is forcibly inserted into theanti-shaft-release groove 331 c by elastic deformation and the rotaryshaft 331 is driven into the housing 337 through the radial bearing 333until the bearing support section 331 a abuts the thrust bearing 346.Thus, the rotary shaft 331 is rotatably supported by the thrust bearing346 and the radial bearing 333 in the housing 337.

After the rotary shaft 331 is driven into the housing 337, the housing337 is filled with lubricating oil 342. When filling the housing 337with lubricating oil 342, the housing 337, in which the rotary shaft 331is arranged, is put into a filling tank 355 that contains lubricatingoil 356 as shown in FIG. 37. Then, the filling tank 355 now containingthe housing is subjected to vacuum suctioning, using a vacuum device.The housing 337 is filled with lubricating oil 342 as the filling tankthat is subjected to vacuum suctioning is taken out into the atmosphere.

At this time, the housing 337 is filled with lubricating oil 342 in sucha way that, lubricating oil 342 is prevented from leaking to the outsideof the housing 337 through the shaft receiving hole 341 when it isexpanded by a temperature change and the gap 345 formed between therotary shaft 331 and the shaft receiving hole 341 is free from aninsufficiently filled condition when the lubricating oil 342 there iscontracted by a temperature change. In short, the surface level of thelubricating oil 342 in the gap 345 is made to always be found within theshaft receiving hole 341 regardless of temperature changes.

Because an operation of vacuum suctioning is carried out by using avacuum device for filling the housing 337 with the lubricating oil 342,the pressure in the inside of the housing 337 is lower than that of theoutside of the housing. As a result, the lubricating oil 342 isprevented from leaking to the outside of the housing 337.

In the bearing unit 330 of this embodiment, because the radial bearing333 is made of sintered metal, the radial bearing 333 is filled withlubricating oil 342 and the dynamic pressure generating grooves 358 thatis adapted to generate dynamic pressure when the rotary shaft 331 isdriven to revolve is also filled with lubricating oil 342. In short, allthe spaces in the housing 337 are filled with lubricating oil 342.

While the housing of the above described bearing unit is formed bymolding, using synthetic resin, the material of the housing is notlimited to synthetic resin. For example, the housing may alternativelybe formed by molding a mixture of a moldable metal material and asynthetic resin material or some other molding material that can bemolded by means of a metal mold. However, it should be noted that, whenthe housing is formed by using a material other than synthetic resin,there may be a risk that the contact angle of the lubricating oil filledin the housing relative to the inner peripheral surface of the shaftreceiving hole becomes insufficient. The risk that the contact angle oflubricating oil becomes insufficient can be avoided by applying asurface active agent to the inner peripheral surface of the shaftreceiving hole or to the entire outer peripheral surface of the topclosure section including the inner peripheral surface of the shaftreceiving hole.

While the thrust bearing is formed as part of the housing in the abovedescribed bearing unit, a bottom closure section that is provided with athrust bearing may be formed separately from the housing main body andthe bottom closure section and the housing main body may be bondedtogether by means of an appropriate technique such as heat seal orultrasonic seal.

A bearing unit 330 having the above described configuration dissolvesthe problem of a so-called shaft opposite ends open type bearing unithaving a seamless resin-made housing that is very effective forpreventing lubricating oil leakage but accompanied by a drawback thatlubricating oil is apt to be pushed out when the shaft is driven torevolve and simultaneously the residual air and the air dissolved in thelubricating oil expand (cavitation phenomenon).

While the housing of a conventional bearing unit of the type underconsideration is formed by a plurality of components and the passage wayprovided to short circuit the pressurized air at the opposite ends ofthe radial bearing follows a route of the closed side of theshaft—passage way—outside of the housing—the open side of the shaft, thecorresponding passage way of a bearing unit according to the inventionis made to follow a route of the closed side of the shaft—communicationpassage way—the open side of the shaft and the space-forming member 334in which the communication passage way is formed is surrounded andcovered by a seamless housing 337.

Thus, the bearing unit 330 is provided with a space-forming member 334and a communication passage way 350 running by the upper end and thelower end of the radial bearing 333 so as to follow a route connectingthe bearing lower end—passage way—bearing upper end in order toalleviate any reduction in the static pressure at the closed side, orthe lower end of the closed side. Therefore, it is possible to preventleakage of lubricating oil that can be caused by the residual air tryingto push up lubricating oil. Additionally, since the gap between therotary shaft and the housing is the sole path connecting the inside andthe outside of the housing, it is possible to prevent lubricating oilfrom dispersing if it is subjected to impact. In other words, it ispossible to prevent the viscous fluid from oozing out. As a result, thebearing unit 330 can maintain its excellent lubricating performance fora long period of time.

The space-forming member of a bearing unit according to the inventionmay alternatively have a configuration as shown in FIG. 38. In thefollowing description, the components of the bearing unit that are sameas or similar to their counterparts of the bearing unit 330 of FIG. 19are denoted respectively by the same reference symbols and will not bedescribed in detail.

The bearing unit 370 of FIG. 38 differs from the bearing unit 330 ofFIG. 19 in terms of the configuration of space-forming member. In thebearing unit 370, the space-forming member 371 includes a firstspace-forming member 372 formed to surround an upper part of the lateralsection and the top section of the radial bearing 333 and a secondspace-forming member 373 formed to surround a lower part of the lateralsection and the bottom section of the radial bearing 333. The firstspace-forming member 372 is provided at the center thereof with a shaftreceiving hole 372 a, through which a rotary shaft 331 is driven intothe housing so as to be rotatably supported by the radial bearing 333.

The second space-forming member 373 is provided at the center of theinner surface of the bottom section thereof with a thrust bearing 346for rotatably supporting the bearing support section 331 a of the rotaryshaft 331, which is arranged at an end of the rotary shaft 331 in thethrusting direction. The thrust bearing is integrally formed by moldingwith the space-forming member 371, which is made of resin. The thrustbearing 346 is formed as a pivot bearing that supports the bearingsupport section 331 a having a curved or tapered profile of the rotaryshaft 331 at a single point.

A communication passage way is formed between the space-forming member371 and the radial bearing 333 as in the case of the bearing unit 330.The communication passage way operates to make the opposite ends of thethrust bearing of the rotary shaft 331, which projects from the radialbearing 333, communicate with each other. In other words, thecommunication passage way 350 makes one end of the shaft, which is theclosed end where the thrust bearing 346 is formed, and the other end ofthe shaft, which is the open end located close to the shaft receivinghole 372 a of the first space-forming member 372, communicate with eachother.

Like the bearing unit 330, the bearing unit 370 is provided with aspace-forming member and a communication passage way running by theupper end and the lower end of the radial bearing 333 so as to follow aroute connecting the bearing lower end—passage way—bearing upper end inorder to alleviate any reduction in the static pressure at the closedside, or the lower end of the closed side. Therefore, it is possible toprevent leakage of lubricating oil that can be caused by the residualair trying to push up lubricating oil. Additionally, since the gapbetween the rotary shaft and the housing is the sole path connecting theinside and the outside of the housing, it is possible to preventlubricating oil from dispersing if it is subjected to impact. In otherwords, it is possible to prevent the viscous fluid from oozing out. As aresult, the bearing unit 370 can maintain its excellent lubricatingperformance for a long period of time.

In a bearing unit according to the invention, the space-forming membermay have any configuration so long as resin does not flow into thecommunication passage way that is formed between the space-formingmember and the radial bearing when the housing member is formed byouterset molding. Otherwise, the configuration of the space-formingmember is not subjected to any limitations.

A bearing unit according to the invention as described above is adaptedto use lubricating oil as viscous fluid to be filled in the housing.However, viscous fluid of any other type may alternatively be selectedand used for the purpose of the invention so long as it shows viscosityand surface tension to a predetermined extent.

The present invention is by no means limited to the above-describedembodiments, which may be modified and altered in various different waysthat are apparent to those who are skilled in the art without departingfrom the scope of the invention.

INDUSTRIAL APPLICABILITY

As described above, according to the invention, there is provided abearing unit that is compact and highly reliable and can enjoy a longservice life because it is free from both the problem of a slipping outshaft at the time of assembling and the problem of leakage oflubricating oil.

While a bearing unit according to the invention is highly reliable andcan enjoy a long service life because it is free from the problem ofleakage of lubricating oil, it is not accompanied by a drawback ofremarkable complexity in terms of device configuration and manufacturingprocess.

Additionally, a bearing unit according to the invention is made tocomprise an anti-shaft-release member and a member for securing anecessary space around the anti-shaft-release member in order to preventthe rotary shaft from slipping away due to impact or a change in theatmospheric pressure and/or the inner pressure.

Still additionally, the housing member of a bearing unit according tothe invention is made of a polymeric material so as to hold theremaining members including a seal member from outside without any gapin order to prevent lubricating oil from leaking.

Still additionally, a hydrodynamic fluid bearing is used as radialbearing means of a bearing unit according to the invention so that therotary shaft can be supported highly accurately and the bearing unit isfree from problems caused by leakage of lubricating oil, while thethrust bearing means has a simple configuration, to a great advantage ofreducing the number of components, the manufacturing steps and hence themanufacturing cost.

Still additionally, in a bearing unit according to the invention, thedrawing pressure is made greater in the inside of the gap surroundingthe rotary shaft so that lubricating oil can hardly leak out from thegap and the lubricating oil in the gap is made free from a biaseddistribution caused when the rotary shaft becomes eccentric, whichconsequently improves the reliability of the bearing unit.

Furthermore, a bearing unit according to the invention can effectivelyreduce vibrations and the configuration of the thrust bearing means issimplified because of the use of an anti-shaft-release member and amember for securing a necessary space around the anti-shaft-releasemember.

Finally, a bearing unit according to the invention can find applicationsas bearing in the field of motors of heat-emitting devices, spindlemotors of disc drives and other motors. It can be used in a mechanismfor supporting a rotary shaft or a mechanism for supporting a part thatrevolves relative to a shaft.

1-8. (canceled)
 9. A bearing unit having a shaft and bearing means forrotatably supporting the shaft, comprising: a lubricating oil sealmember arranged between the shaft and the bearing means with a gapinterposed between them; and a housing member made of synthetic resinfor holding the lubricating oil seal member and the bearing means fromthe outer peripheries thereof.
 10. The bearing unit according to claim9, wherein a radial bearing means for bearing the radial load beingapplied to the shaft and a thrust bearing means for bearing the thrustload being applied to the shaft are provided as the bearing means, andfurther comprising: an anti-shaft-release member attached to said shaft,and a space-forming member provided separately from the lubricating oilseal member in order to secure a space around said anti-shaft-releasemember, wherein the radial bearing means, the lubricating oil sealmember and the space-forming member are held by the housing member. 11.The bearing unit according to claim 9, wherein the housing member ismade of a polymeric material.
 12. The bearing unit according to claim10, wherein a hydrodynamic fluid bearing is used as the radial bearingmeans.
 13. The bearing unit according to claim 10, wherein the thrustbearing means is realized by making an end of the shaft to show a curvedprofile and bringing it into contact with the second member.
 14. Thebearing unit according to claim 9, wherein the part of the shaft adaptedto form a gap with the lubricating oil seal member is tapered so as tohave a diameter that increases toward the inside of the shaft.
 15. Thebearing unit according to claim 10, wherein a hydrodynamic fluid bearingis formed as the thrust bearing means by using the anti-shaft-releasemember and the space-forming member.
 16. A rotary drive comprising arotary body, a shaft adapted to revolve with the rotary body, bearingmeans for rotatably supporting the shaft and drive means for driving therotary body to revolve, wherein a lubricating oil seal member arrangedso as to produce a gap between the shaft and a housing member made ofsynthetic resin for peripherally holding the member and the bearingmeans are provided.
 17. The rotary drive according to claim 16, whereinradial bearing means for bearing the radial load being applied to theshaft and thrust bearing means for bearing the thrust load being appliedto the shaft are provided as the bearing means, and further comprising:an anti-shaft-release member attached to said shaft, and a space-formingmember provided separately from the lubricating oil seal member in orderto secure a space around the anti-shaft-release member, wherein theradial bearing means, the lubricating oil seal member and thespace-forming member are held by the housing member.
 18. The rotarydrive according to claim 16, wherein the housing member is made of apolymeric material.
 19. The rotary drive according to claim 17, whereina hydrodynamic fluid bearing is used as the radial bearing means. 20.The rotary drive according to claim 17, wherein the thrust bearing meansis realized by making an end of the shaft to show a curved profile andbringing it into contact with the second member.
 21. The rotary driveaccording to claim 16, wherein the part of the shaft adapted to form agap with the lubricating oil seal member is tapered so as to have adiameter that increases toward the inside of the shaft.
 22. The rotarydrive according to claim 17, wherein a hydrodynamic fluid bearing isformed as the thrust bearing means by using the anti-shaft-releasemember and the space-forming member. 23-29. (canceled)